The target is incorrectly set when broadcasting jobs to monero miners
### Description

The target is incorrectly set when broadcasting jobs to monero miners. Both [XMRRig ](https://github.com/xmrig/xmrig) and [xmr-stak](https://github.com/fireice-uk/xmr-stak) throw errors indicating that the target provided by miningcore is incorrect.
The target sent by miningcore is always "00000000"

xmr-stak returns

`[2020-08-10 19:44:47] : Fast-connecting to 127.0.0.1:3052 pool ...
[2020-08-10 19:44:47] : Pool 127.0.0.1:3052 connected. Logging in...
[2020-08-10 19:44:47] : SOCKET ERROR - [127.0.0.1:3052] PARSE error: Invalid target of length 8`

xmrig returns

`[127.0.0.1:3052] login error code: 5`

### Steps to Reproduce

1. Run monero daemon and wallet daemon
2. Run miningcore
3. Run XMRStak

### Expected behavior

xmrstak receives job

### Actual behavior

xmrstak errors due to format/content of target

### Reproduces how often

Always 

### Version

master commit : d72db18e797d53c6f80441117c8f0aca348910ef

### Additional Information

monero pool configuration:
```
"pools": [
      {
          // DON'T change the id after a production pool has begun collecting shares!
          "id": "monero",
          "enabled": true,
          "coin": "monero",
          // Address to where block rewards are given (pool wallet)
          "address": "redacted",
          // How often to poll RPC daemons for new blocks, in milliseconds
          "blockRefreshInterval": 400,
          "rewardRecipients": [
            {
                // Pool wallet
                "address": "redacted",
                "percentage": 1
            }
        ],
          // Some miner apps will consider the pool dead/offline if it doesn't receive
          // anything new jobs for around a minute, so every time we broadcast jobs,
          // set a timeout to rebroadcast in this many seconds unless we find a new job.
          // Set to zero to disable. (Default: 0)
          "jobRebroadcastTimeout": 10,
          // Remove workers that haven't been in contact for this many seconds.
          // Some attackers will create thousands of workers that use up all available
          // socket connections, usually the workers are zombies and don't submit shares
          // after connecting. This features detects those and disconnects them.
          "clientConnectionTimeout": 600,
          // If a worker is submitting a high threshold of invalid shares, we can
          // temporarily ban their IP to reduce system/network load.
          "banning": {
              "enabled": true,
              // How many seconds to ban worker for
              "time": 600,
              // What percent of invalid shares triggers ban
              "invalidPercent": 50,
              // Check invalid percent when this many shares have been submitted
              "checkThreshold": 50
          },
          // Each pool can have as many ports for your miners to connect to as you wish.
          // Each port can be configured to use its own pool difficulty and variable
          // difficulty settings. 'varDiff' is optional and will only be used for the ports
          // you configure it for.
          "ports": {
              // Binding port for your miners to connect to
              "3052": {
                  // Binding address (Default: 127.0.0.1)
                  "listenAddress": "0.0.0.0",
                  // Pool difficulty
                  "difficulty": 0.02,
                  // TLS/SSL configuration
                  "tls": false,
                  "tlsPfxFile": "/var/lib/certs/mycert.pfx",
                  // Variable difficulty is a feature that will automatically adjust difficulty
                  // for individual miners based on their hash rate in order to lower
                  // networking overhead
                  "varDiff": {
                      // Minimum difficulty
                      "minDiff": 0.01,
                      // Maximum difficulty. Network difficulty will be used if it is lower than
                      // this. Set to null to disable.
                      "maxDiff": null,
                      // Try to get 1 share per this many seconds
                      "targetTime": 15,
                      // Check to see if we should retarget every this many seconds
                      "retargetTime": 90,
                      // Allow time to very this % from target without retargeting
                      "variancePercent": 30,
                      // Do not alter difficulty by more than this during a single retarget in
                      // either direction
                      "maxDelta": 500
                  }
              }
          },
          // Recommended to have at least two daemon instances running in case one drops
          // out-of-sync or offline. For redundancy, all instances will be polled for
          // block/transaction updates and be used for submitting blocks. Creating a backup
          // daemon involves spawning a daemon using the "-datadir=/backup" argument which
          // creates a new daemon instance with it's own RPC config. For more info on this,
          // visit: https:// en.bitcoin.it/wiki/Data_directory and
          // https:// en.bitcoin.it/wiki/Running_bitcoind
          "daemons": [
              {
                  "host": "127.0.0.1",
                  "port": 18081,
                  "wallet":"redacted",
                  "user": "redacted",
                  "password": "redacted"
              },
              {
                "host": "127.0.0.1",
                "port": 42069,
                "wallet":"redacted",
                "user": "redacted",
                "password": "redacted",
                "category":"wallet"
            }
          ],
          // Generate payouts for recorded shares
          "paymentProcessing": {
              "enabled": true,
              // Minimum payment in pool-base-currency (ie. Bitcoin, NOT Satoshis)
              "minimumPayment": 0.01,
              "payoutScheme": "PPLNS",
              "payoutSchemeConfig": {
                  "factor": 2.0
              }
          }
      }
  ]

```



relevant bit of xmr-stak poos.txt:

`"pool_list" :
[
	{"pool_address" : "127.0.0.1:3052", "wallet_address" : "47NqeUGKmpTcDndfnpJWrc8XkUSSYTKbBJEzqkVdVB3S8a7QdZBKASRWmADLnTPRViECLDPxFv3XN2M7svxt3i8rEh6EYns", "rig_id" : "", "pool_password" : "x", "use_nicehash" : false, "use_tls" : false, "tls_fingerprint" : "", "pool_weight" : 1 },
],`

content of job:

```
{
  "result": {
    "id": "0HM1C4PIFEO05",
    "job": {      
      "blob": "0c0ccbe7d2f8050ea3d590e4ee3726a8b2bb540fbf064b491c9ab6c4540ba189b72ab9cfd424e00000000004b9cc518ab2fa791041ff022ca17f5a08b9c0c70876ff799da13f56a9342c6e29",
      "height": 2145830
      "job_id": "17",
      "target": "00000000",
    },
    "status": "OK"
  }
  "error": null,
  "id": 1
}
```