Exclude rake files from blocklength cop
Exclude rake files from blocklength cop

This is a new addition and seems a little heavy handed.  It looks like there
will be [a refinement in future](https://github.com/bbatsov/rubocop/issues/3772)
to make this work a little better.

alphagov/collections-publisher,alphagov/collections-publisher,alphagov/collections-publisher