chore(travis): run tests on node v6 instead of 0.x
chore(travis): run tests on node v6 instead of 0.x

eslint v3 dropped support for node < 4 and
I do not care enough to built some fancy logic
on when to run aslant on the CI

code should still be able to run on any
node version prior to v4.

janraasch/javascript-commitment