Fix whitespace
Remove Gemfile.lock, this is a library

`Gemfile.lock` should should not be checked in for gems.

See the article "Clarifying the Roles of the .gemspec and Gemfile" [1] from
one of the authors of Bundler.

[1]: http://yehudakatz.com/2010/12/16/clarifying-the-roles-of-the-gemspec-and-gemfile/
Use Bundler to build and install the gem

Bundler is already used by coco (see the `Gemfile`) and is the standard
tool for all gem-related things. Let's use the provided Bundler
Rake tasks instead of rolling our own.
Integrate default Bundler .gitignore
Remove custom bundler command fro Travis

Bundler is already declared as a development dependency
Merge branch 'gioele-gemspec-cleanup' into development