minor: fix Gemfile to specify activesupport < 4.0 if using < 1.9.3

Author: estolfo

Gemfile

@@ -3,7 +3,11 @@ source 'https://rubygems.org'
 gem 'json'
 gem 'rake', :require => ['rake/testtask']
 gem 'rake-compiler', :require => ['rake/extensiontask', 'rake/javaextensiontask']
-gem 'activesupport'
+if RUBY_VERSION < '1.9.3'
+  gem 'activesupport', '~>3.0'
+else
+  gem 'activesupport'
+end
 
 group :deploy do
   gem 'git'