Make YAML::ENGINE syck under ruby 1.9 to fix travis 1.9 build issue

config/boot.rb

@@ -2,6 +2,11 @@
 #   licensed under the Affero General Public License version 3 or later.  See
 #   the COPYRIGHT file.
 
+if RUBY_VERSION.include?("1.9")
+  require 'yaml'
+  YAML::ENGINE.yamler= 'syck'
+end
+
 require 'rubygems'
 
 # Set up gems listed in the Gemfile.