Require Rails 4+ to ensure the fix from #400 will apply properly and …

…bump a minor version accordingly

jbuilder.gemspec

@@ -1,15 +1,15 @@
 Gem::Specification.new do |s|
   s.name     = 'jbuilder'
-  s.version  = '2.6.4'
-  s.authors  = ['David Heinemeier Hansson']
-  s.email    = ['david@37signals.com']
+  s.version  = '2.7.0'
+  s.authors  = 'David Heinemeier Hansson'
+  s.email    = 'david@basecamp.com'
   s.summary  = 'Create JSON structures via a Builder-style DSL'
   s.homepage = 'https://github.com/rails/jbuilder'
   s.license  = 'MIT'
 
   s.required_ruby_version = '>= 1.9.3'
 
-  s.add_dependency 'activesupport', '>= 3.0.0'
+  s.add_dependency 'activesupport', '>= 4.0.0'
   s.add_dependency 'multi_json',    '>= 1.2'
 
   s.files         = `git ls-files`.split("\n")