chore(builder): update heroku-buildpack-grails to v19

See heroku/heroku-buildpack-grails@v17...v19

Author: mboersma

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

@@ -33,7 +33,7 @@ download_buildpack https://github.com/heroku/heroku-buildpack-ruby.git
 download_buildpack https://github.com/heroku/heroku-buildpack-nodejs.git         v75
 download_buildpack https://github.com/heroku/heroku-buildpack-java.git           v38
 download_buildpack https://github.com/heroku/heroku-buildpack-gradle.git         v12
-download_buildpack https://github.com/heroku/heroku-buildpack-grails.git         v17
+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-php.git            v75