chore(travis): unlock node.js versions
chore(travis): unlock node.js versions

Fixes #3586
mozilla/fxa-content-server,swatilk/fxa-content-server,swatilk/fxa-content-server,mozilla/fxa-content-server,vladikoff/fxa-content-server,vladikoff/fxa-content-server,shane-tomlinson/fxa-content-server,swatilk/fxa-content-server,shane-tomlinson/fxa-content-server,shane-tomlinson/fxa-content-server,mozilla/fxa-content-server,vladikoff/fxa-content-server