Update .gitlab-ci.yml

.gitlab-ci.yml

-image: maven:3.6.3-jdk-8
+image: debian:jessie
 
 
 build:
     script:
+        - echo "deb http://ppa.launchpad.net/webupd8team/java/ubuntu xenial main" | tee /etc/apt/sources.list.d/webupd8team-java.list
+        - echo "deb-src http://ppa.launchpad.net/webupd8team/java/ubuntu xenial main" | tee -a /etc/apt/sources.list.d/webupd8team-java.list
+        - apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys EEA14886
         - apt-get update
-        - apt-get install openjfx=8u161-b12-1ubuntu2 libopenjfx-java=8u161-b12-1ubuntu2 libopenjfx-jni=8u161-b12-1ubuntu2
+        - apt-get install oracle-java8-installer
+        - apt-get install maven
         - mvn package -B
         
 release: