Clean up code style issues in Gemfile, Rakefile and *.gemspec.

* use single quotes
* use the new Ruby 1.9.3 hash syntax
* use $LOAD_PATH instead of $.
* use fail instead of raise for system exceptions
Merge pull request #2980 from braingourmets/cleanup/codestyle

Clean up code style issues in Gemfile, Rakefile and *.gemspec.