chore(buildpacks): update heroku-buildpack-python to v99

See heroku/heroku-buildpack-python@v97...v99

Author: mboersma

rootfs/builder/install-buildpacks

@@ -37,6 +37,6 @@ download_buildpack https://github.com/heroku/heroku-buildpack-java.git
 download_buildpack https://github.com/heroku/heroku-buildpack-nodejs.git         v98      07-nodejs
 download_buildpack https://github.com/heroku/heroku-buildpack-php.git            v119     08-php
 download_buildpack https://github.com/heroku/heroku-buildpack-play.git           v26      09-play
-download_buildpack https://github.com/heroku/heroku-buildpack-python.git         v97      10-python
+download_buildpack https://github.com/heroku/heroku-buildpack-python.git         v99      10-python
 download_buildpack https://github.com/heroku/heroku-buildpack-ruby.git           v153     11-ruby
 download_buildpack https://github.com/heroku/heroku-buildpack-scala.git          v75      12-scala