update ruby version

rspec-rails-swagger.gemspec

@@ -12,7 +12,7 @@ Gem::Specification.new do |s|
   s.files       = Dir['*.md', '*.txt', 'lib/**/*']
   s.homepage    = 'https://github.com/drewish/rspec-rails-swagger'
 
-  s.required_ruby_version = '~> 2.0'
+  s.required_ruby_version = Gem::Requirement.new(">= 2.3.0")
   s.add_runtime_dependency 'rails', '>= 3.1'
   s.add_runtime_dependency 'rspec-rails'
 end