Remove jeweler and use .gemspec

* Cleans up the Rakefile
* Preps up the .gemspec for completion
* Use HTTPS for RubyGems
* Specify `activesupport` dependency for different Ruby versions
* Remove 1.9.2 on Travis
Merge pull request #10 from duggiefresh/gemspec

Fixes #9 - Remove jeweler and use .gemspec