title: Gitlab-CE docker build faild "unknown instruction"
body: <p>I am using a self hosted Gitlab-CE Server. I try to use a CI Pipeline with three stages: build, package, deploy</p>
  
  <p>Build is a maven task - that works. </p>
  
  <p>In the package task I try to build the docker container. But this step fails with the following error: </p>
  
  <pre><code>Error response from daemon: Dockerfile parse error line 1: unknown instruction: &lt;!DOCTYPE
  </code></pre>
  
  <p>That is my .gitlab-ci.yml (Without deploy step)</p>
  
  <pre><code>image: docker:latest
  services:
    - docker:dind
  
  variables:
    SPRING_PROFILES_ACTIVE: gitlab-ci
  
  stages:
    - build
    - package
    - deploy
  
  maven-build:
    image: maven:3-jdk-8
    stage: build
    script: "mvn package -B"
    artifacts:
      paths:
        - target/*.jar
  
  docker-build:
    stage: package
    script:
    - docker login -u gitlab-ci-token -p $CI_BUILD_TOKEN https://devel.priv.net
    - docker build -t https://devel.priv.net/d.p/service-discovery
    - docker push https://devel.priv.net/d.p/service-discovery
  </code></pre>
  
  <p>The gitlab Server can be reached at <a href="https://devel.priv.net" rel="nofollow noreferrer">https://devel.priv.net</a>. The Repository is <a href="https://devel.priv.net/d.p/service-discovery" rel="nofollow noreferrer">https://devel.priv.net/d.p/service-discovery</a>
  It is protected via username and password. </p>
  
  <p>What is wrong in my configuration? </p>