Pin java buildpack back to system

Author: cweibel

java-hello/manifest.yml

@@ -2,7 +2,7 @@
 applications:
 - name: test-java-hello
   buildpacks:
-  - https://github.com/cloudfoundry/java-buildpack.git#feature/go-migration
+  - java_buildpack
   random-route: true
   memory: 768M
   path: target/hello-world-0.0.1-SNAPSHOT.jar