Lock sprockets to 2.11.0 until a fix is available & Bump version

If we don't do this then all systems that update to 2.12 will break.

related to https://github.com/Compass/compass-rails/issues/144
Update compass-rails.gemspec
Fix for dependency.
Merge pull request #146 from nadavshatz/1-1-stable

Locking sprockets to 2.11 and bumping the version for now.