Reverted Java CI Image to  maven:3.6-jdk-8

Change-Id: Ieebaefaba0658bdb774fca955c791f361d72585f
Signed-off-by: Thomas Psota <thomas.psota@iese.fraunhofer.de>
diff --git a/Jenkinsfile_CX b/Jenkinsfile_CX
index f096d67..3638544 100644
--- a/Jenkinsfile_CX
+++ b/Jenkinsfile_CX
@@ -25,7 +25,7 @@
     - name: PGDATA
       value: /run/postgresql/data
   - name: java
-    image: iesetps/basyx-ci-java:latest
+    image: maven:3.6-jdk-8
     resources:
       requests:
         memory: "3Gi"