[SETUP] Depend on Mocha 0.13, older versions throw exceptions about `…

…mocha/setup`

Please make sure to delete your Gemfile.lock and run `bundle`.

The "shoulda" gem depends on "bourne", which only recently
[upgraded](https://github.com/thoughtbot/bourne/commits/v1.3.0)
to Mocha 0.13.1.

tire.gemspec

@@ -36,7 +36,7 @@ Gem::Specification.new do |s|
   #
   s.add_development_dependency "bundler",      "~> 1.0"
   s.add_development_dependency "shoulda"
-  s.add_development_dependency "mocha"
+  s.add_development_dependency "mocha",        "~> 0.13"
   s.add_development_dependency "minitest",     "~> 2.12"
   s.add_development_dependency "activerecord", ">= 3.0"
   s.add_development_dependency "mongoid",      "~> 2.2"