Updates to Gemfile to clean it up.

Gemfile

@@ -1,32 +1,36 @@
-require 'rbconfig'
 source 'https://rubygems.org'
 
+this_ruby = Gem::Version.new(RUBY_VERSION)
+ruby_230 = Gem::Version.new('2.3.0')
+
 # Add dependencies required to use your gem here.
-gem "thor", ">= 0.14.0"
+gem 'thor', '>= 0.14.0'
 
 # Add dependencies to develop your gem here.
 # Include everything needed to run rake, tests, features, etc.
 group :development do
-  gem "rake", ">= 0.8.7"
-  gem "rspec", "~> 3.5.0"
-  gem "guard"
-  gem "guard-rspec"
-  gem "rb-readline", "~> 0.5.0"
-  gem "test_construct"
-  gem "capture-output", "~> 1.0.0"
-  if RbConfig::CONFIG['host_os'] =~ /linux|freebsd|openbsd|sunos|solaris/
+  gem 'capture-output', '~> 1.0.0'
+  gem 'coveralls', require: false
+  gem 'guard'
+  gem 'guard-rspec'
+  gem 'jeweler', '>= 1.6.2', '< 2.2' if this_ruby < ruby_230
+  gem 'jeweler', '>= 1.6.2' if this_ruby >= ruby_230
+  gem 'rake', '>= 0.8.7'
+  gem 'rb-readline', '~> 0.5.0'
+  gem 'rspec', '~> 3.5.0'
+  gem 'rubocop'
+  gem 'test_construct'
+
+  install_if -> { RUBY_PLATFORM =~ /linux|freebsd|openbsd|sunos|solaris/ } do
     gem 'libnotify'
   end
-  if RbConfig::CONFIG['host_os'] =~ /darwin|mac os/
+
+  install_if -> { RUBY_PLATFORM =~ /darwin/ } do
     gem 'terminal-notifier-guard', '~> 1.7.0'
   end
-  gem "coveralls", require: false
-  gem "rubocop"
-  if RUBY_VERSION < '2.3.0'
-    gem "rack", "< 2"
-    gem "listen", "< 3"
-    gem "jeweler", ">= 1.6.2", "< 2.2"
-  else
-    gem "jeweler", ">= 1.6.2"
+
+  install_if -> { this_ruby < ruby_230 } do
+    gem 'listen', '< 3'
+    gem 'rack', '< 2'
   end
 end