Only support Ruby >= 1.9.3

Update the README, Gemfiles, and gemspec to remove all references to
Rubies < 1.9.3.

.travis.yml

@@ -1,8 +1,6 @@
 language: ruby
 
 rvm:
-  - 1.8.7
-  - 1.9.2
   - 1.9.3
   - 2.0.0
   - 2.1

Gemfile

@@ -1,8 +1,2 @@
 source "https://rubygems.org"
 gemspec
-
-if Gem::Version.new(RUBY_VERSION.dup) < Gem::Version.new('1.9.3')
-  gem 'i18n', '< 0.7'
-  gem 'rest-client', '~> 1.6.8'
-  gem 'activesupport', '~> 3.2'
-end

README.rdoc

@@ -32,14 +32,7 @@ If you want to build the gem from source:
 
 == Requirements
 
-* Ruby 1.8.7 or above. (Ruby 1.8.6 may work if you load
-  ActiveSupport.) For Ruby versions before 1.9.2, you'll need to add this to your Gemfile:
-
-    if Gem::Version.new(RUBY_VERSION) < Gem::Version.new('1.9.2')
-      gem 'rest-client', '~> 1.6.8'
-    end
-
-
+* Ruby 1.9.3 or above.
 * rest-client, json
 
 == Bundler

gemfiles/default-with-activesupport.gemfile

@@ -1,10 +1,4 @@
 source "https://rubygems.org"
 gemspec :path => File.join(File.dirname(__FILE__), "..")
 
-if Gem::Version.new(RUBY_VERSION) < Gem::Version.new('1.9.3')
-  gem 'i18n', '< 0.7'
-  gem 'rest-client', '~> 1.6.8'
-  gem 'activesupport', '~> 3.2'
-else
-  gem 'activesupport'
-end
+gem 'activesupport'

gemfiles/json.gemfile

@@ -1,12 +1,5 @@
 source "https://rubygems.org"
 gemspec :path => File.join(File.dirname(__FILE__), "..")
 
-if Gem::Version.new(RUBY_VERSION) < Gem::Version.new('1.9.3')
-  gem 'i18n', '< 0.7'
-  gem 'rest-client', '~> 1.6.8'
-  gem 'activesupport', '~> 3.2'
-else
-  gem 'activesupport'
-end
-
+gem 'activesupport'
 gem 'json'

gemfiles/yajl.gemfile

@@ -1,12 +1,5 @@
 source "https://rubygems.org"
 gemspec :path => File.join(File.dirname(__FILE__), "..")
 
-if Gem::Version.new(RUBY_VERSION) < Gem::Version.new('1.9.3')
-  gem 'i18n', '< 0.7'
-  gem 'rest-client', '~> 1.6.8'
-  gem 'activesupport', '~> 3.2'
-else
-  gem 'activesupport'
-end
-
+gem 'activesupport'
 gem 'yajl-ruby'

stripe.gemspec

@@ -5,6 +5,7 @@ require 'stripe/version'
 spec = Gem::Specification.new do |s|
   s.name = 'stripe'
   s.version = Stripe::VERSION
+  s.required_ruby_version = '>= 1.9.3'
   s.summary = 'Ruby bindings for the Stripe API'
   s.description = 'Stripe is the easiest way to accept payments online.  See https://stripe.com for details.'
   s.authors = ['Ross Boucher', 'Greg Brockman']