Downgrade Listen to 1.3.x

This is so that we can be Ruby 1.8.x compatible.

jekyll.gemspec

@@ -25,7 +25,7 @@ Gem::Specification.new do |s|
 
   s.add_runtime_dependency('liquid', "~> 2.5.2")
   s.add_runtime_dependency('classifier', "~> 1.3")
-  s.add_runtime_dependency('listen', "~> 2.0")
+  s.add_runtime_dependency('listen', "~> 1.3.0")
   s.add_runtime_dependency('maruku', "~> 0.6.0")
   s.add_runtime_dependency('pygments.rb', "~> 0.5.0")
   s.add_runtime_dependency('commander', "~> 4.1.3")