Remove Gemfile.lock from repository

See:
http://yehudakatz.com/2010/12/16/clarifying-the-roles-of-the-gemspec-and-gemfile/
Updated build matrix for most common scenarios

* Ruby 1.8.7, 1.9.3, 2.0.0, 2.1.0
* Rails 3.2, 4.0, master
Updated asset tests to better test for js and css

Switched to testing for aspects of the library itself instead of the
project's preamble (which apparently changes).
Fixed the Fancybox integration test

It looks like elements of the test changed, so updated the test to
reflect those changes
Added test for image assets
Dropped Ruby 1.8.7 from build matrix

Too many development dependencies have dropped Ruby 1.8
support (nokogiri, capybara, rubyzip). It's not worth the maintenance
costs.
Merge pull request #23 from rmm5t/fix-travis-build-matrix

Fix travis build matrix