Handle 304 status for remote config files

[daniloisr]

Hi all, when using remote config I was facing the following error:

bad URI(is not URI?):

On lines lib/rubocop/remote_config.rb:48-49:

when Net::HTTPRedirection
  request(URI.parse(response['location']), limit - 1, &block)

This happens for 304 HTTPNotModified responses, which don't have the 'location' key.
(and to help reviewers, 304 responses occurs due this header)

So my solution is to just handle this response and reuses the existing cached file.

[bbatsov]

The fix looks good, but it should be listed in the changelog.

[daniloisr]

@bbatsov done

[mikegee]

@daniloisr add yourself to the bottom of the changelog too to get the build to pass.

[bbatsov]

👍