Add secure rubygem.org address and Devise secret key in the test suite

Bundle install was returning a message advising a change to the HTTPS version of rubygem.org.

And the spec was failing based upon the Devise secret key missing. 
If I am reading the TavisCI information correctly [build 16](https://travis-ci.org/brianhempel/mongo_session_store/builds/12635945) is failed because of the Devise problem.