Update rubocop dependency to >= 0.23

.rubocop.yml

@@ -1,5 +1,5 @@
 AllCops:
-  Includes:
+  Include:
     - 'Gemfile'
     - 'Rakefile'
     - 'gems.gemspec'

.travis.yml

@@ -1,13 +1,7 @@
-before_install:
-  - gem update bundler
-  - bundle --version
-  - gem update --system 2.1.11
-  - gem --version
 bundler_args: --without development
 language: ruby
 rvm:
   - 1.8.7
-  - 1.9.2
   - 1.9.3
   - 2.0.0
   - 2.1.0

Gemfile

@@ -17,7 +17,7 @@ group :test do
   gem 'coveralls', :require => false
   gem 'json', :platforms => [:rbx, :ruby_19, :ruby_18]
   gem 'mime-types', '~> 1.25', :platforms => [:jruby, :ruby_18]
-  gem 'rubocop', '>= 0.16', :platforms => [:ruby_19, :ruby_20, :ruby_21]
+  gem 'rubocop', '>= 0.23', :platforms => [:ruby_19, :ruby_20, :ruby_21]
   gem 'rspec', '>= 2.11'
   gem 'simplecov', :require => false
   gem 'webmock'

Rakefile

@@ -8,10 +8,10 @@ task :test => :spec
 
 begin
   require 'rubocop/rake_task'
-  Rubocop::RakeTask.new
+  RuboCop::RakeTask.new
 rescue LoadError
   task :rubocop do
-    $stderr.puts 'Rubocop is disabled'
+    $stderr.puts 'RuboCop is disabled'
   end
 end