string.c: minor grammar fix [ci skip]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@53509 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
string.c: minor grammar fix [ci skip]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@53509 b2dd03c8-39d4-4d8f-98ff-823fe69b080e