improve CI caching

.gitlab-ci.yml

 image: golang:1.13
 
+variables:
+  GOPATH: "$CI_PROJECT_DIR/.gopath"
 
 cache:
   paths:
     - .gopath/
     - ui/assets_vfsdata.go
-
-before_script:
-  - mkdir -p .gopath
-  - export GOPATH="$CI_PROJECT_DIR/.gopath"
-  - go generate ./ui
-
+  key: default
+  policy: pull
 
 stages:
-  - vet
+  - prepare
   - test
   - build
 
 
-vet:
-  stage: vet
+prepare:
+  stage: prepare
+  cache:
+    policy: pull-push
   script:
+    - mkdir -p .gopath
+    - export GOPATH="$CI_PROJECT_DIR/.gopath"
+    - go generate ./ui
     - go vet ./...
 
 
@@ -93,9 +96,14 @@ docker:
   image:
     name: gcr.io/kaniko-project/executor:debug
     entrypoint: [""]
-  before_script: []
+  cache:
+    paths:
+      - .docker/cache
+    key: default
+    policy: pull-push
   script:
+    - mkdir -p $CI_PROJECT_DIR/.docker/cache
     - echo "{\"auths\":{\"index.docker.io\":{\"auth\":\"$DOCKER_HUB_AUTH\"}}}" > /kaniko/.docker/config.json
-    - /kaniko/executor --context $CI_PROJECT_DIR --dockerfile $CI_PROJECT_DIR/Dockerfile --destination autoradio/tank:$CI_COMMIT_REF_NAME
+    - /kaniko/executor --cache=true --cache-dir $CI_PROJECT_DIR/.docker/cache --context $CI_PROJECT_DIR --dockerfile $CI_PROJECT_DIR/Dockerfile --destination autoradio/tank:$CI_COMMIT_REF_NAME
   only:
     - master