Fix running on sprockets-rails master#322

Merged

rmosolgo merged 3 commits intoreactjs:masterfrom

vipulnsward:sprockets-3-compat

Jul 23, 2015

Commits on Jul 18, 2015

- Assets version and register_engine have been moved from app.assets to app.config.assets on sprockets
vipulnsward
committed
- Use Sprockets.register_engine if we are on latest master
vipulnsward
committed

Commits on Jul 23, 2015

- DRY up setting of Sprockets config
vipulnsward
committed