Fix up Twitter client configuration

This has changed in version 5 of the Twitter gem, see
https://github.com/sferik/twitter/blob/master/README.md#configuration
for details
Should probably bump the version

Does this count as a breaking change?
Pin version

I think this is probably safe
Break out into separate method
Pin to 5.0
Merge pull request #3 from pikesley/new-twitter-config