migrating to https api

According to Untappd API Mailing list the http endpoint for the V4 API will stop working on Oct 1 .  https://groups.google.com/forum/#!topic/untappd-api-developer-group/LHVB_P-5EOU

I've verified that the https endpoint is already available and working
Merge pull request #7 from clickonchris/master

@clickonchris thanks for the pull request. I'll push a new gem out soon.