chore(builder): update heroku-buildpack-scala to v60

See heroku/heroku-buildpack-scala@v55...v60

Author: mboersma

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

@@ -38,5 +38,5 @@ download_buildpack https://github.com/heroku/heroku-buildpack-play.git
 download_buildpack https://github.com/heroku/heroku-buildpack-python.git         v58
 download_buildpack https://github.com/heroku/heroku-buildpack-php.git            v67
 download_buildpack https://github.com/heroku/heroku-buildpack-clojure.git        v66
-download_buildpack https://github.com/heroku/heroku-buildpack-scala.git          v55
+download_buildpack https://github.com/heroku/heroku-buildpack-scala.git          v60
 download_buildpack https://github.com/heroku/heroku-buildpack-go.git             6eeb09f