chore(builder): update heroku-buildpack-python to v70

See heroku/heroku-buildpack-python@v62...v70

Author: mboersma

builder/rootfs/usr/local/src/slugbuilder/builder/install-buildpacks

@@ -35,7 +35,7 @@ download_buildpack https://github.com/heroku/heroku-buildpack-java.git
 download_buildpack https://github.com/heroku/heroku-buildpack-gradle.git         v12
 download_buildpack https://github.com/heroku/heroku-buildpack-grails.git         v19
 download_buildpack https://github.com/heroku/heroku-buildpack-play.git           v24
-download_buildpack https://github.com/heroku/heroku-buildpack-python.git         v62
+download_buildpack https://github.com/heroku/heroku-buildpack-python.git         v70
 download_buildpack https://github.com/heroku/heroku-buildpack-php.git            v75
 download_buildpack https://github.com/heroku/heroku-buildpack-clojure.git        v68
 download_buildpack https://github.com/heroku/heroku-buildpack-scala.git          v60