Bg/isolate import of parser to avoid conflicts

I'm asking for this small change as it resolves a problem we have been running into when using RuboCop in a rails application with a variety of gems.

A few of the other gems defines a module Parser. When running 

    bundle exec rubocop

in this environment, we get the error 'Module Parser does not have a method check_for_encoding_support'.

We did try reordering gems in the Gemfile, but this did not help. Changing to `require_relative` from `require` did.

Many thanks - if you know a better way to fix this, I'd be happy to help!