rubocop update for cook-3900

This is meant to complement #138.

There are still some issues on this branch that I wasn't sure how to deal with - 
```
Ambiguous regexp literal. Parenthesize the method arguments if it's surely a regexp literal, or add a whitespace to the right of the / if it should be a division.
```
Not sure which solution is right for these, but they are all in tests.

The commit regarding pulling over spec tests was reverted for now, since the tests are still under development.