Remove and ignore gemfiles

These are automatically generated by `appraisal`/`rake`. See also:
https://github.com/thoughtbot/shoulda/pull/232.
Sort .gitignore
Merge branch 'ignore_gemfiles' of https://github.com/sferik/shoulda into sferik-ignore_gemfiles

# By Erik Michaels-Ober
# Via Erik Michaels-Ober
* 'ignore_gemfiles' of https://github.com/sferik/shoulda:
  Sort .gitignore
  Remove and ignore gemfiles

Conflicts:
	gemfiles/3.0.gemfile
	gemfiles/3.0.gemfile.lock
	gemfiles/3.1.gemfile
	gemfiles/3.1.gemfile.lock
	gemfiles/3.2.gemfile
	gemfiles/3.2.gemfile.lock