text: Title: Update kneed
  Body: The [kneed](https://github.com/arvkevi/kneed) library has been updated a couple of times (with bugfixes!) since it was incorporated into the yellowbrick code. I would like to update the knee finding algorithm to be consistent with the [0.7.0 release](https://github.com/arvkevi/kneed/releases/tag/v0.7.0) of kneed.
  
  Would you welcome a PR to update the code? Thanks!