Fix dependencies that break with ruby 1.9.3

Ruby 1.9.3 requires a recent version of RSpec 2, and simplecov
supercedes rcov on ruby 1.9+.

Gemfile

@@ -6,10 +6,10 @@ gem "thor", ">= 0.14.0"
 # Add dependencies to develop your gem here.
 # Include everything needed to run rake, tests, features, etc.
 group :development do
-  gem "rake"
-  gem "rspec", "~> 2.1.0"
+  gem "rake", "~> 0.8.7"
+  gem "rspec", "~> 2.10"
   gem "jeweler", ">= 1.6.2"
-  gem "rcov", ">= 0"
+  gem "rcov", :platforms => :mri_18
+  gem "simplecov", :platforms => :mri_19
   gem "test-construct"
-  gem "ruby-debug"
 end