replace find_by with find_by_email to be compatible with rails 3.2
Fix Rails 3.2 uncompatibility: find_by
Refactor give preference to Rails 4 method

Thanks to AhmedAttyah for the suggestion,
see https://github.com/gonzalo-bulnes/simple_token_authentication/pull/7#issuecomment-31232889
Bump version number
Merge branch 'fix-rails-3.2-uncompatible-find-by'