Upgrade thin gem to the v1.5.1

I can only upgrade to v1.5.1 because of a dependency in renee on
rack v1.3.0.

The following gems are also upgraded because of dependencies:
* renee
* eventmachine
* minitest

I need this upgrade to be able to install gitdocs on a Debian wheezy system( thin 1.3.1 will not compile according to [Bug#676211](http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=676211). 

Seems to be working so far, and no code changes were required so I think that it is ready to merge.


(P.S.: Thanks for writing this gem! I have been using to sync multiple repositories, between multiple machines for the last few years. gitdocs handled multiple repos, file system notifications, and desktop notifications at a time when I could not find any other projects that did this.

If you are still supporting this gem, and accepting PRs, I am interested in doing more work on this gem.)