rubocop >=3.0? Remove unnecessary rubocop exclusion

[gavindidrichsen]

Context.

PR https://github.com/puppetlabs/rspec-puppet/pull/80/files excluded a deprecated rubocop Rspec/FilePath cop because this will be deprecated in the next major release of rubocop. See here for more information.

This issue is a placeholder to remove the exclusion in due course

[gavindidrichsen]

Closing this off as this will be part of work later