Remove `node` from Travis scripts.
Remove `node` from Travis scripts.

This package is only testing browser related things, no need
to run in each supported node version.

When we add SSR testing, we will bring this back (and add Node 4).

glimmerjs/glimmer.js,glimmerjs/glimmer.js,glimmerjs/glimmer.js,glimmerjs/glimmer.js