Update .gitlab-ci.yml (jdk 8)

.gitlab-ci.yml

+variables:
+  JAVA_HOME: "/usr/lib/jvm/java-8-openjdk-amd64/"
+
+
 build:
     script:
-        - "mvn package -B"
\ No newline at end of file
+        - mvn package -B
\ No newline at end of file