update micro demo to new buffer methods

Author: noopkat

tests/demos/micro.js

@@ -2,7 +2,7 @@ var Avrgirl = require('../../avrgirl-arduino');
 var board = {
   name: 'micro',
   baud: 57600,
-  signature: new Buffer([0x43, 0x41, 0x54, 0x45, 0x52, 0x49, 0x4e]),
+  signature: Buffer.from([0x43, 0x41, 0x54, 0x45, 0x52, 0x49, 0x4e]),
   productId: ['0x0037', '0x8037', '0x0036'],
   protocol: 'avr109'
 };