Use custom docker image

.gitlab-ci.yml

 default:
-  image: maven:latest
+  image: thebeggs/simplewebapp-base:latest
+  username: $DOCKER_HUB_USERNAME
+  password: $DOCKER_HUB_TOKEN
+  email: $DOCKER_HUB_EMAIL
 
 variables:
   PORT: "5000"
 
 build:
   stage: build
-  before_script:
-    - apt-get update
-    - apt-get install -qq -y pandoc texlive
   script:
     - mvn compile
 
 test:
   stage: test
-  before_script:
-    - apt-get update
-    - apt-get install -qq -y pandoc texlive
   script:
     - mvn test