chore(buildpacks): update heroku-buildpack-ruby to v167

See heroku/heroku-buildpack-ruby@v164...v167

Author: mboersma

rootfs/builder/install-buildpacks

@@ -38,5 +38,5 @@ download_buildpack https://github.com/heroku/heroku-buildpack-nodejs.git
 download_buildpack https://github.com/heroku/heroku-buildpack-php.git            v121     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         v109     10-python
-download_buildpack https://github.com/heroku/heroku-buildpack-ruby.git           v164     11-ruby
+download_buildpack https://github.com/heroku/heroku-buildpack-ruby.git           v167     11-ruby
 download_buildpack https://github.com/heroku/heroku-buildpack-scala.git          v76      12-scala