Add Travis CI support

[martindsouza]

https://docs.travis-ci.com/user/languages/javascript-with-nodejs/

https://docs.travis-ci.com/user/for-beginners/

[vincentmorneau]

Simple .travis.yml example here: https://github.com/OraOpenSource/apex-nitro/blob/master/.travis.yml

[martindsouza]

From @vincentmorneau

XO: https://github.com/xojs/xo - JS Linter
AVA: https://github.com/avajs/ava - JS Testing framework