WIP Gemfile: Update Rake and Mocha

All gems are now up to date. The following changes were copied from the
gem's respective changelog that may pertain to us:

```
Rake changes:

* The rake task arguments can contain escaped commas (10.1)
* Restored Ruby 1.8.7 compatibility (10.2)

Mocha changes:

* Consider stubs on superclasses if none exist on primary receiver. Largely based
  on changes suggested by @ccutrer in #145. Note: this may break existing tests
  which rely on the old behavior
```

* Remove minitest-colorize in favor of minitest-reporter.
* Use twiddle-waka for Minitest's version to ensure safe version updates

On my local machine, I was able to shave 6 seconds off the test suite. I was also not able to encounter the `ln` issue from #4990

![1 _tmux__usersnanodevelopercodenanofiles_tmux_2014-06-19_17-26-57_2014-06-19_17-27-00](https://cloud.githubusercontent.com/assets/1889575/3335469/8176ba5a-f815-11e3-9ba0-b8110f6d6e0e.jpg)

Refs: #4984 #4990