* string.c (dispose_string): use rb_str_free for freeing string in
  parse.y. by Sokolov Yura <funny.falcon@gmail.com>
  https://github.com/ruby/ruby/pull/87 fix GH-87

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@38774 b2dd03c8-39d4-4d8f-98ff-823fe69b080e