Fix travis CI

Hello there. Just noticed you have a travis integration going, but it errors out, and does not run any tests.

This pull request fixes that. I considered adding that flashy "build passing" badge to the README as well, but that would be up to you I guess :)

By the way, I removed testing for node 0.11, since node-usb is known to not work (nonolith/node-usb#39)

Thanks for this tool, I'll check it out once my tessel reaches my mailbox.