First attempt at pushing to Docker Hub

.gitlab-ci.yml

@@ -21,12 +21,24 @@ variables:
   # When using dind, it's wise to use the overlayfs driver for
   # improved performance.
   DOCKER_DRIVER: overlay2
-  IMAGE_TAG: grav:$CI_COMMIT_REF_NAME
 
 before_script:
   - docker info
+  - docker login -u "$CI_REGISTRY_USER" -p "$CI_REGISTRY_PASSWORD" $CI_REGISTRY
+
+build-master:
+  stage: build
+  script:
+    - docker build --pull -t $CI_REGISTRY_IMAGE .
+    - docker push "$CI_REGISTRY_IMAGE"
+  only:
+    - master
 
 build:
   stage: build
   script:
-    - docker build --pull -t $IMAGE_TAG .
+    - docker build --pull -t "$CI_REGISTRY_IMAGE:$CI_COMMIT_REF_NAME" .
+    - docker push "$CI_REGISTRY_IMAGE:$CI_COMMIT_REF_NAME"
+  except:
+    - master
+