Remove Gemfile.lock

When developing a gem, use the gemspec method in your Gemfile to avoid
duplication. In general, a gem’s Gemfile should contain the Rubygems source
and a single gemspec line. Do not check your Gemfile.lock into version
control, since it enforces precision that does not exist in the gem
command.

Source: http://yehudakatz.com/2010/12/16/clarifying-the-roles-of-the-gemspec-and-gemfile/
Remove trailing whitespace
Remove jquery-rails dependency

The jquery-cookie library depends on jquery in order to function, but
jquery can be provided by many means other than the jquery-rails gem.

The dependency on jquery rails was also unnecessarily restrictive in its
versioning.
Remove runtime dependencies on thor and version

These aren't required anywhere, so I can't find any evidence they are
used. They certainly don't need to be runtime dependencies.
Remove rails 3.0 generator

The gem already has a dependency on railties >= 3.2, so a generator
aimed at 3.0 isn't helping anyone.