Docker commant not found.

Hello guys,

I keep getting: /bin/bash: line 56: docker: command not found with following gitlab ci yaml defintion:

image: docker:latest

stages:
  - test
  - build

before_script:
  - apt-get update -yqq
  - apt-get install apt-transport-https -yqq
  - echo "deb http://dl.bintray.com/sbt/debian /" | tee -a /etc/apt/sources.list.d/sbt.list
  - apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv 642AC823
  - apt-get update -yqq
  - apt-get install sbt -yqq
  - sbt sbt-version

test:
  image: java:8
  stage: test
  script:
    - sbt scalastyle && sbt test:scalastyle && sbt clean test

build:
  image: java:8
  stage: build
  script:
    - docker login -u gitlab-ci-token -p $CI_BUILD_TOKEN registry.gitlab.com/moncalamari
    - sbt server/docker:publish

Basically, the build needs java:8 to run sbt and docker to publish images to gitlab Repository via sbt docker plugin. Any clues?

Thanks!