remove rspec-rails version

rspec-rails-swagger.gemspec

@@ -14,5 +14,5 @@ Gem::Specification.new do |s|
 
   s.required_ruby_version = '~> 2.0'
   s.add_runtime_dependency 'rails', '>= 3.1'
-  s.add_runtime_dependency 'rspec-rails', '~> 3.0'
+  s.add_runtime_dependency 'rspec-rails'
 end