CI: Build Rugged on OS X.
CI: Bump the ruby 2.1.x version.
CI: Allow the Rubinius builds to fail.
CI: Allow the OS X build with Ruby 2.1.2 to fail.
CI: Specify the Rubinius version more tightly.
CI: Building with 2.1.2 on OS X is broken.

Don’t even try to build with it.