Enable Style/SpaceAroundEqualsInParameterDefault cop

What does this MR do?

Enable a new rubocop cops as discussed here: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/1877#note_13529646

Are there points in the code the reviewer needs to double check?

May be a good idea to send a message to people to prevent master red because of the new cop.

Why was this MR needed?

We want to improve code style and not waste endbosses time checking style manually

What are the relevant issue numbers?

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• CHANGELOG entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the style guides
• Branch has no merge conflicts with master (if you do - rebase it please)
• Squashed related commits together