Remove deprecation warning (#21)
Remove deprecation warning (#21)

`Parser::Rewriter` is [deprecated](https://github.com/whitequark/parser/blob/fbe0e8cbec557c96b0e0f4a8c5201155ee478284/lib/parser/rewriter.rb#L6), so we should update to `Parser::TreeRewriter`.
dgollahon/rspectre,dgollahon/rspectre