Update syntax from StandardRb specification and specify ActiveSupport version

[D-system]

This PR fixes:

• 284

• 280

Changes proposed in this pull request:

• Update syntax in accordance with StandardRb
  • Remove redundant returns
  • Remove unnecessary parentheses
  • Use double quotes
  • Invert condition to not mix logical operator in an unless
  • Ignore UselessRescue because used for test purposes
• Lock ActiveSupport to pass the tests (code from https://github.com/Data-Liberation-Front/csvlint.rb/pull/279)

Fix #284 Fix #280

[Floppy]

Thanks for all these fixes @D-system, I'll try to get them all merged in this week. ❤️

[D-system]

@Floppy Thanks James for merging and keep maintaining the gem. With the tests passing, it is easier to contribute now.