Add support for HipChat APIv2

This bumps the requirement for the hipchat gem up to >= 1.0.0, where the
APIv2 functionality was first added. In the interest of backwards
compatibility, it explicitly keeps the default API version at v1, in
case the hipchat gem ever switches its default to v2.
Merge pull request #232 from michaelherold/add-hipchat-api-v2

Add support for HipChat APIv2