* ext/json: merge JSON 1.7.7.
  This includes security fix. [CVE-2013-0269]
  https://github.com/flori/json/commit/d0a62f3ced7560daba2ad546d83f0479a5ae2cf2
  https://groups.google.com/d/topic/rubyonrails-security/4_YvCpLzL58/discussion

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39208 b2dd03c8-39d4-4d8f-98ff-823fe69b080e