chore(buildpacks): update heroku-buildpack-go to v50

See heroku/heroku-buildpack-go@v49...v50

Author: mboersma

rootfs/builder/install-buildpacks

@@ -39,4 +39,4 @@ download_buildpack https://github.com/heroku/heroku-buildpack-python.git
 download_buildpack https://github.com/heroku/heroku-buildpack-php.git            v112
 download_buildpack https://github.com/heroku/heroku-buildpack-clojure.git        v75
 download_buildpack https://github.com/heroku/heroku-buildpack-scala.git          v72
-download_buildpack https://github.com/heroku/heroku-buildpack-go.git             v49
+download_buildpack https://github.com/heroku/heroku-buildpack-go.git             v50