remove '//' style comments.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@65466 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
remove '//' style comments.
following build log: https://travis-ci.org/ruby/ruby/jobs/448551951
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@65466 b2dd03c8-39d4-4d8f-98ff-823fe69b080e