Necessary upgrades for Rails 6 and Ruby 2.7

Thi fixes #41 (closed). Hey @marnen, would you mind check if this works for you? I'll start using the gem for a major project, so I'll probably add new features in the near future.

Created by: marnen

@crashtech Thanks! Sorry I haven’t been working on this. I’ll try this version of the gem on that project and let you know how it works.