* ext/psych/yaml/yaml.h: [DOC] merge upstream typo fix by @GreenGeorge
  https://github.com/tenderlove/psych/pull/161


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42993 b2dd03c8-39d4-4d8f-98ff-823fe69b080e