Fix intermittently failing spec

* `fog_spec.rb:328` fails intermittently due to a race condition
* Use [TimeCop][1] gem to freeze time during the spec
* Extract magic number
* Break long line

[1]: https://github.com/travisjeffery/timecop

![TimeCop
Poster](http://www.deconstructingmovies.com/wp-content/uploads/2014/03/timecop-poster.jpg)
Move Timecop gem from Gemfile into gemspec
Merge pull request #1531 from thoughtbot/ap-fix-spec

Fix intermittently failing spec