Current pingCommand is useless for macOS
### Issue
Mac status is not working because in sleep state the ping command is always successful.

I could use a command like `ssh user@192.168.1.256 'if [[$ (pmset -g powerstate IODisplayWrangler | tail -1 | cut -c29) -lt 4]]; then; echo 0; else; exit 1; fi;'`
but the current execution of pingCommand doesn't make any sense to it

### Environment
* os & os version: macos catalina 10.15.5
* node version: v12.18.2
* homebridge version: 1.1.1
* homebridge-wol version: 4.2.1

### Configuration
My configuration looks like this:
```
    "accessories": [
        {
            "name": "Macbook Pro 2017",
            "ip": "192.168.1.256",
            "pingInterval": 45,
            "pingCommand": "ssh user@192.168.1.256 'if [[ $(pmset -g powerstate IODisplayWrangler | tail -1 | cut -c29) -lt 4 ]]; then; echo 0; else; exit 1; fi;'",
            "mac": "XX:XX:XX:XX:XX:XX",
            "broadcastAddress": "192.168.1.256",
            "wakeGraceTime": 10,
            "wakeCommand": "ssh user@192.168.1.256 caffeinate -u -t 300",
            "shutdownCommand": "ssh user@192.168.1.256 pmset sleepnow",
            "shutdownGraceTime": 15,
            "log": true,
            "logPinger": true,
            "debugLog": true,
            "returnEarly": false,
            "accessory": "NetworkDevice"
        }
    ],
```
