Make Travis Runs Faster
Make Travis Runs Faster

See https://docs.travis-ci.com/user/workers/container-based-infrastructure/.

Also, updates node to v4, the current LTS.

PolymerLabs/incremental-dom,PolymerLabs/incremental-dom,sparhami/incremental-dom,google/incremental-dom,jridgewell/incremental-dom,PolymerLabs/incremental-dom,google/incremental-dom,jridgewell/incremental-dom,jridgewell/incremental-dom,sparhami/incremental-dom,sparhami/incremental-dom,sparhami/incremental-dom,google/incremental-dom