Update Mozilla Rhino to 1.7R4

https://play.lighthouseapp.com/projects/82401/tickets/949-update-rhino-to-17r4

We are at the moment running 1.7R2 but since then mozilla have changed the namespace.

The newest version is "org.mozilla" % "rhino" % "1.7R4"

The reason I wan't to upgrade is that 1.7R4 has better support for ecmascript 5 and I was not successful when trying to compile ember.js with 1.7R2
But as soon as I switched to 1.7R4 it worked like a charm. Why you might ask? Primarily it seems to boil down to ember.js using a lot of ecmascript 3's reserved keywords such as volatile, char, string... but in ecmascript 5 they have released these keywords into the wild.