Remove jeweler/ fix tests

Running into a jruby error even when testing against MRI. This fixes the issue by only requiring jruby in the Gemfile where a platform option can be specified instead of in the gem spec.

Removing jeweler allows us to to be more flexible with our gemspec and it wasn't really all that needed.
Merge pull request #147 from schneems/schneems/fix-gemfile-require-weirdness

Remove jeweler/ fix tests