title: I2C output error when sending an array
body: <p>I have recently started using Node-RED in a Raspberry Pi and my quest is to connect to a couple of I2C devices with the use of the node-red-contrib-i2c package. 
  One action which I am trying to do is to send an array of integers to the I2C device with the I2C output node but I always get the error </p>
  
  <p><code>TypeError: String.isString is not a function</code></p>
  
  <p>I have tried a couple of different syntax but without success. I have included an export of the flow below.</p>
  
  <pre><code>[{"id":"d2a2b073.e222c","type":"function","z":"e442e95f.6c2b98","name":"","func":"msg.address = 96;\nmsg.command = 48;\nmsg.payload = [85,85];\nreturn msg;","outputs":1,"noerr":0,"x":316,"y":243,"wires":[["7061e7e7.ac6f98","65101109.cf323"]]},{"id":"ce6f4bff.3bf998","type":"inject","z":"e442e95f.6c2b98","name":"","topic":"","payload":"","payloadType":"date","repeat":"","crontab":"","once":false,"x":126,"y":244,"wires":[["d2a2b073.e222c"]]},{"id":"7061e7e7.ac6f98","type":"debug","z":"e442e95f.6c2b98","name":"","active":true,"console":"false","complete":"true","x":539,"y":263,"wires":[]},{"id":"65101109.cf323","type":"i2c out","z":"e442e95f.6c2b98","name":"","i2cdevice":"3d751c57.1120f4","address":"96","command":"","payload":"","count":"2","x":567,"y":223,"wires":[]},{"id":"3d751c57.1120f4","type":"i2c-device","z":"","device":"/dev/i2c-1","address":"100"}]
  </code></pre>
  
  <p>An example of the msg.payload sent:</p>
  
  <pre><code>msg.address = 96;
  msg.command = 48;
  msg.payload = [85,85];
  return msg;
  </code></pre>