Add Ruby 2.5 Support/Require Ruby 2.2+ (#12)

* Add Ruby 2.5 Support

* Remove gemnasium badge

* Define required_ruby_version

.travis.yml

@@ -2,6 +2,7 @@ language: ruby
 cache: bundler
 rvm:
   - 2.2.5
-  - 2.3.1
-  - 2.4.0
+  - 2.3.7
+  - 2.4.5
+  - 2.5.3
 before_install: gem update bundler

README.md

@@ -4,7 +4,6 @@
 [![Build Status](https://travis-ci.org/toshimaru/rack-simple_user_agent.svg)](https://travis-ci.org/toshimaru/rack-simple_user_agent)
 [![Coverage Status](https://coveralls.io/repos/github/toshimaru/rack-simple_user_agent/badge.svg)](https://coveralls.io/github/toshimaru/rack-simple_user_agent)
 [![Code Climate](https://codeclimate.com/github/toshimaru/rack-simple_user_agent/badges/gpa.svg)](https://codeclimate.com/github/toshimaru/rack-simple_user_agent)
-[![Dependency Status](https://gemnasium.com/badges/github.com/toshimaru/rack-simple_user_agent.svg)](https://gemnasium.com/github.com/toshimaru/rack-simple_user_agent)
 
 Rack::SimpleUserAgent is Rack::Request extension which detects user-agent from user-agent string. No complicated logic for the detection, it simply(stupidly) checks if user-agent includes particular string or not.
 

rack-simple_user_agent.gemspec

@@ -17,6 +17,8 @@ Gem::Specification.new do |spec|
   spec.bindir        = "exe"
   spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
   spec.require_paths = ["lib"]
+
+  spec.required_ruby_version = ">= 2.2.2"
 
   spec.add_development_dependency "bundler", "~> 1.11"
   spec.add_development_dependency "rake", "~> 11.0"