Arrays to buffers

Change our writes to use buffers instead of arrays so node Writable streams don't complain. We haven't seen this issue with node-serialport because it [auto converts arrays to buffers](https://github.com/voodootikigod/node-serialport/blob/master/serialport.js#L162) but other output streams do not.

I can resubmit without the travis.yml changes but they're needed if we're going to get the test suite in order.

-Francis