Fix CI builds

[invalidusrname]

Hey there. I took a stab at fixing the current failing tests on Travis CI.

I tried my best to change as little as possible to everything under /lib, but places where I updated I tried to link to an existing PR or github issue explaining why it was needed.

Other changes:

• remove versions of ruby that have been declared End of Life
• bump gems used for testing (Gemfile)
• bump gems used for testing (tests/test_app/Gemfile)
• fix deprecation warnings in rspec
• add rubocop and format spec directory

Totally open to suggestion on changes here. Thanks!

There's a bunch on commits here. If you wouldn't mind squashing them, I'd appreciate it. I figured it best to leave them in for review so you can understand where my head was 😄

[Da9elKH]

I would really appreciate it if any administrators can look at this pull request, so that the problem in #285 can be solved!

Nice work @invalidusrname!