text: Title: TypeError: Object of type timedelta is not JSON serializable
  Body: In newer versions of python the following line produces and error.
  To fix it convert it to string.
  
  https://github.com/anselal/antminer-monitor/blob/6f9803e891296c0c2807125128532f4d52024c0f/antminermonitor/blueprints/asicminer/asic_antminer.py#L115