Added JUnit test to verify the example
Upgrade Ratpack to 0.9.4-SNAPSHOT for new ChainAction support

The interface for ChainAction has significantly changed in 0.9.4, which
is due out in a few days, so it makes sense to target this.
Moved HandlerBootstrap/ModuleBootstrap logic into HandlerFactory

While doing this, ChainAction was used instead of Action<Chain> as this
gives us more expressive power in Ratpack 0.9.4
Remove stray blank line
Remove unused import
Add Java 8 check to build.gradle