Bump arel to 4.0.0
Revert "sprockets 2.9.x doesn't work with uglifier 2.0 yet."

This reverts commit 575838795019f7402992e3bfa83a0c5048cf143d.

Conflicts:
	railties/lib/rails/generators/app_base.rb

Reason: sprockets 2.9.1 fixes this issue
Use latest coffee-rails release
Use the same uglifier version that the generated applications