Prevents crash if user sends invalid JSON data; adds relevant tests

Protects against another way users could currently cause the server to crash: text messages which are not valid JSON.

This adds a few basic tests, which confirm that the server can still respond to a PING from one user, after being sent binary messages or invalid JSON text messages by a different user.

This also adds a Travis CI configuration file, which automatically runs these tests against Node 0.11 and 0.11.

You can see the relevant logs for my branch here: [![Build Status](https://travis-ci.org/jeremybanks/accidentalbot.svg)](https://travis-ci.org/jeremybanks/accidentalbot) If @cliss also enabled Travis for his master repository, this would result in the tests automatically being run against any submitted pull requests.