commit 22430510b9662edd64e3792c560629daf8aebc82
Author: Jan Berkel <jan@soundcloud.com>
Date:   Tue Apr 1 07:00:17 2014 -0400

    Explicitly require 'set'.

diff --git a/lib/syntax/lang/ruby.rb b/lib/syntax/lang/ruby.rb
index edccda0..90eca56 100644
--- a/lib/syntax/lang/ruby.rb
+++ b/lib/syntax/lang/ruby.rb
@@ -1,4 +1,5 @@
 require 'syntax'
+require 'set'
 
 module Syntax