Update Dockerfile

Update to point to the correct base Dockerfile image

Author: carieshmarie

flexible/sparkjava/src/main/docker/Dockerfile

@@ -1,4 +1,4 @@
-FROM gcr.io/google_appengine/openjdk8
+FROM gcr.io/google_appengine/openjdk
 VOLUME /tmp
 ADD spark-1.0-jar-with-dependencies.jar app.jar
 CMD [ "java","-Djava.security.egd=file:/dev/./urandom","-jar","/app.jar"]