Add ruby version checking in Gemfile to install needed gems versions (#234)

Author: sagebomb

CHANGELOG.md

@@ -5,6 +5,7 @@
 * [#219](https://github.com/ruby-grape/grape-entity/pull/219): Fix: double pass options in serializable_hash - [@sbatykov](https://github.com/sbatykov).
 * [#226](https://github.com/ruby-grape/grape-entity/pull/226): Added fetch method to fetch from opts_hash - [@alanjcfs](https://github.com/alanjcfs).
 * [#232](https://github.com/ruby-grape/grape-entity/pull/232), [#213](https://github.com/ruby-grape/grape-entity/issues/213): Added `#kind_of?` and `#is_a?` to `OutputBuilder` to get an exact class of an `output` object - [@avyy](https://github.com/avyy).
+* [#234](https://github.com/ruby-grape/grape-entity/pull/234), [#233](https://github.com/ruby-grape/grape-entity/issues/233): Added ruby version checking in `Gemfile` to install needed gems versions for supporting old rubies too - [@avyy](https://github.com/avyy).
 * Your contribution here.
 
 0.5.1 (2016-4-4)

Gemfile

@@ -2,6 +2,22 @@ source 'http://rubygems.org'
 
 gemspec
 
+current_ruby_version = Gem::Version.new(RUBY_VERSION)
+
+if Gem::Requirement.new('>= 2.2.2').satisfied_by? current_ruby_version
+  gem 'activesupport', '~> 5.0'
+  gem 'rack', '~> 2.0', group: [:development, :test]
+else
+  gem 'activesupport', '~> 4.0'
+  gem 'rack', '< 2', group: [:development, :test]
+end
+
+if Gem::Requirement.new('~> 2.0').satisfied_by? current_ruby_version
+  gem 'json', '~> 2.0', group: [:development, :test]
+else
+  gem 'json', '< 2', group: [:development, :test]
+end
+
 group :development do
   gem 'pry'
   gem 'guard'
@@ -13,9 +29,7 @@ end
 
 group :development, :test do
   gem 'rake'
-  gem 'json', '~> 1.8.3'
   gem 'rspec'
-  gem 'rack', '~> 1.6.4'
   gem 'rack-test', '~> 0.6.2', require: 'rack/test'
   gem 'rubocop', '0.31.0'
 end

grape-entity.gemspec

@@ -14,10 +14,8 @@ Gem::Specification.new do |s|
 
   s.rubyforge_project = 'grape-entity'
 
-  s.add_runtime_dependency 'activesupport', '< 5'
   s.add_runtime_dependency 'multi_json', '>= 1.3.2'
 
-  s.add_development_dependency 'rake'
   s.add_development_dependency 'maruku'
   s.add_development_dependency 'yard'
   s.add_development_dependency 'rspec', '~> 2.9'