Gemfile.lock should not be committed for a gem

"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, which is used to install gems in practice. Even if the
precision could be enforced, you wouldn’t want it, since it would
prevent people from using your library with versions of its dependencies
that are different from the ones you used to develop the gem."

http://yehudakatz.com/2010/12/16/clarifying-the-roles-of-the-gemspec-and-gemfile/
Merge pull request #1 from ministryofjustice/remove_gem_lock

Gemfile.lock should not be committed for a gem