Test against master branch of runtime dependency

[zetachang]

Currently we got three runtime dependencies,

• opal
• opal-activesupport
• react-rails

It will be nice if we could test against the master branch of those gems. And with cron jobs support of travis, we could discover breakage sooner even before they release new versions.

Setup for opal is done, will add support to others in recent weeks.

[catmando]

Good idea!

[janbiedermann]

Good idea!