Added Rake development dependency for Travis-CI

omniauth-cas.gemspec

@@ -17,6 +17,7 @@ Gem::Specification.new do |gem|
 
   gem.add_dependency 'omniauth', '~> 1.0'
 
+  gem.add_development_dependency 'rake', '~> 0.9'
   gem.add_development_dependency 'simplecov', '~> 0.5.4'
   gem.add_development_dependency 'rspec', '~> 2.7'
   gem.add_development_dependency 'rack-test', '~> 0.6'