Workaround for Ruby 2.2.0.

Hi, I'm CRuby commiter. We'll remove ```YAML::EngineManager``` and ```YAML::ENGINE``` from Ruby 2.2.0. See. https://bugs.ruby-lang.org/issues/8344

Some yaml files couldn't parse by psych. I hope to use syck gem after 2.2.0 release. I fixed ```YAML::EngineManager``` on syck gem.

PS. syck master seems to broken for new releases. I'll fix another pull requests.

/cc @tenderlove