Update processor.js

Fixes old call to `this.options.logger` in processor.

Fixes crash:
```
/home/simon/public_html/node-clementine-server/node_modules/fluent-ffmpeg/lib/processor.js:631
      this.options.logger.warn('No running ffmpeg process, cannot send signal'
                          ^
TypeError: Cannot call method 'warn' of undefined
    at FfmpegCommand.proto.kill (/home/simon/public_html/node-clementine-server/node_modules/fluent-ffmpeg/lib/processor.js:631:27)
    at Player.stop (/home/simon/public_html/node-clementine-server/lib/player.js:91:18)
    at FfmpegCommand.<anonymous> (/home/simon/public_html/node-clementine-server/lib/player.js:38:8)
    at FfmpegCommand.emit (events.js:98:17)
    at emitEnd (/home/simon/public_html/node-clementine-server/node_modules/fluent-ffmpeg/lib/processor.js:415:16)
    at endCB (/home/simon/public_html/node-clementine-server/node_modules/fluent-ffmpeg/lib/processor.js:564:15)
    at handleExit (/home/simon/public_html/node-clementine-server/node_modules/fluent-ffmpeg/lib/processor.js:155:11)
    at ChildProcess.<anonymous> (/home/simon/public_html/node-clementine-server/node_modules/fluent-ffmpeg/lib/processor.js:169:11)
    at ChildProcess.emit (events.js:98:17)
    at Process.ChildProcess._handle.onexit (child_process.js:810:12)
```