Updated dependencies

I noticed that Virtus has backports locked at ~> 2.6.1. However, the latest version of Backports is 2.7.1.

I set out to update the backports dependency and run the specs, but it turns out I couldn't even bundle in a fresh clone without updating several other dependencies.

I've tested with updated dependencies, and ```rake spec```, ```rake ci```, and ```rake ci:metrics``` all run fine.