Remove 1.9.3 from test matrix and test for minimum ruby version.
Add turbo sprockets to gemfile to speed up asset compilation.
Merge pull request #802 from NatTuck/kill-ruby-1.9

Remove 1.9.3 from test matrix and test for minimum ruby version.
Merge pull request #805 from NatTuck/turbo-sprockets

Add turbo sprockets to gemfile to speed up asset compilation.