change (ci): target cache; new CI image

.gitlab-ci.yml

@@ -2,20 +2,17 @@ stages:
   - test
   - build
 
-image:                             parity/rust-builder:latest
-
 variables:
   GIT_STRATEGY:                    fetch
   GIT_SUBMODULE_STRATEGY:          recursive
   GIT_DEPTH:                       3
   CARGO_INCREMENTAL:               0
-  CARGO_HOME:                      "/ci-cache/${CI_PROJECT_NAME}/cargo/${CI_JOB_NAME}"
-  SCCACHE_DIR:                     "/ci-cache/${CI_PROJECT_NAME}/sccache"
+  CARGO_TARGET_DIR:                "/ci-cache/${CI_PROJECT_NAME}/targets/${CI_COMMIT_REF_NAME}/${CI_JOB_NAME}"
   CI_SERVER_NAME:                  "GitLab CI"
   RUST_TOOLCHAIN:                  "stable"
 
 .docker-env:                       &docker-env
-  image:                           parity/rust-builder:latest
+  image:                           paritytech/ci-linux:production
   before_script:
     - cargo -vV
     - rustc -vV