Add reference to rubocop-rails so we can use the Rails cops

[bunnymatic]

Problem

We had specified some Rails cop rules at the bottom of rubocop.yml but we
did not include the rubocop-rails rules at the top so rubocop was complaining:

Error: unrecognized cop Rails/ApplicationRecord found in .rubocop.yml, unrecognized cop Rails/HasAndBelongsToMany found in .rubocop.yml, unrecognized cop Rails/RakeEnvironment found in .rubocop.yml

Solution

Add to the require line rubocop-rails so those cops will be defined before we read the rubocop.yml file.

Note: this means projects that include this file may need to add rubocop-rails to their Gemfiles

[mattbrictson]

I agree; we either add the rubocop-rails requirement or we remove all of the Rails/* cop configs. This seems like the best option.

[bunnymatic]

Based on a discussion today - it seems that the way raygun works, it will point to this remote file so as soon as this is merged, we may cause issues down the line (to apps that point to this file remotely).

Should we still merge? @christiannelson, thoughts?

I guess we have no easy way of notifying all the consumers, right?