Mac Mini now waking up or impossible to shutdown
### Backstory
I did the setup of my Mac Mini in the WOL plugin.

### Issue
The Mac is recognize as online or offline, but when i try to start or shutdown, i have an error,

### Environment
* os & os version: Mac OS Catalina 10.15.5
* node version: 12.16.2 (Docker in Synology)
* homebridge version: Hoobs 3.2.6
* homebridge-wol version: 4.1.2

### Configuration
My configuration looks like this:
        {
            "accessory": "NetworkDevice",
            "name": "Galaxy-iMac",
            "mac": "mac-address",
            "ip": "192.168.1.5",
            "pingInterval": 45,
            "wakeGraceTime": 10,
            "wakeCommand": "ssh 192.168.1.5 caffeinate -u -t 300",
            "shutdownGraceTime": 15,
            "shutdownCommand": "ssh 192.168.1.5 sudo shutdown -h now",
            "plugin_map": {
                "plugin_name": "homebridge-wol",
                "index": 0
            }

IMPORTANT!
Remove any mac addresses from the configuration by 
exchanging them with <mac-address>
```

### Log
When I follow these steps:
1. Run `DEBUG=* homebridge`
2. Let it run for five minutes
3. Tap a switch
4. Wait one minute
5. Tap the same switch

I get the following log:
```
[Galaxy-iMac] An error occured while trying to wake "Galaxy-iMac" (192.168.1.5): Error: Command failed: ssh 192.168.1.5 caffeinate -u -t 300
/bin/sh: ssh: not found

    at ChildProcess.exithandler (child_process.js:303:12)
    at ChildProcess.emit (events.js:310:20)
    at maybeClose (internal/child_process.js:1021:16)
    at Socket.<anonymous> (internal/child_process.js:443:11)
    at Socket.emit (events.js:310:20)
    at Pipe.<anonymous> (net.js:672:12)
 {
  killed: false,
  code: 127,
  signal: null,
  cmd: 'ssh 192.168.1.5 caffeinate -u -t 300',
  stdout: '',
  stderr: '/bin/sh: ssh: not found\n'
```

### Notes
Thanks for your help
