Fix a missing variable

Author: k0kubun

bin/git-sync-check.rb

@@ -120,7 +120,8 @@ def self.check_consistency
   attempts -= 1
   if attempts > 0
     # Automatically fix inconsistency if it's master, but never sync random new branches.
-    if e.errors.key?('refs/heads/master')
+    ref = 'refs/heads/master'
+    if e.errors.key?(ref)
       remote_ref, local_rev = e.errors['refs/heads/master']
       puts "Fixing inconsistency ref:#{ref.inspect} remote:#{remote_rev.inspect} local:#{local_rev.inspect}"
       unless system('/home/git/git.ruby-lang.org/bin/update-ruby.sh', File.basename(ref))