Support passing RAILS_VERSION for development

Move dynamic development dependencies to Gemfile

Gemfile

@@ -1,3 +1,11 @@
 source 'https://rubygems.org'
+gemspec
 
-gemspec
+compatible_rails_versions = [
+  '>= 3.0.0',
+  ('<5' if Gem::Version.new(RUBY_VERSION) < Gem::Version.new('2.2.2'))
+].compact
+
+gem 'activesupport', (ENV['RAILS_VERSION'] || compatible_rails_versions), require: false
+gem 'i18n', require: false
+gem 'tzinfo', require: false # only needed explicitly for RAILS_VERSION=3

ice_cube.gemspec

@@ -19,7 +19,4 @@ Gem::Specification.new do |s|
 
   s.add_development_dependency('rake')
   s.add_development_dependency('rspec', '~> 2.12.0')
-  s.add_development_dependency('activesupport', ['>= 3.0.0', ('<5' if Gem::Version.new(RUBY_VERSION) < Gem::Version.new('2.2.2'))].compact)
-  s.add_development_dependency('tzinfo')
-  s.add_development_dependency('i18n')
 end

spec/examples/active_support_spec.rb

@@ -1,5 +1,7 @@
 require File.dirname(__FILE__) + '/../spec_helper'
 require 'active_support/time'
+require 'active_support/version'
+require 'tzinfo' if ActiveSupport::VERSION::MAJOR == 3
 
 
 module IceCube