[DOC] Update URL of rurema [ci skip]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63800 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

doc/contributing.rdoc

@@ -334,7 +334,7 @@ a wealth of information available at
 {documenting-ruby.org}[http://documenting-ruby.org/].
 
 There is also the {Ruby Reference
-Manual}[https://bugs.ruby-lang.org/projects/rurema] in Japanese.
+Manual}[https://github.com/rurema/doctree/wiki] in Japanese.
 
 == Contributing A Patch