Ignore exception when plugin not installed

In my Makefile:

```bash
rm_plugins:
	cordova plugin rm org.apache.cordova.core.media-capture
	cordova plugin rm org.apache.cordova.core.device-motion
	cordova plugin rm org.apache.cordova.core.camera
	cordova plugin rm org.apache.cordova.core.file
	cordova plugin rm org.apache.cordova.core.device-orientation
	cordova plugin rm org.apache.cordova.core.network-information
```

If any plugin doesn't installed, it will block my whole target.