chore(gitlab-ci): use npm ci and cache

.gitlab-ci.yml

@@ -9,6 +9,7 @@ default:
     name: fpco/stack-build:lts-16.31
   cache: &global_cache
     paths:
+      - .npm
       - node_modules
       - .stack
       - .stack-work
@@ -44,7 +45,7 @@ npm install:
   stage: setup
   script:
     - ./.npmrc.gup
-    - npm install
+    - npm ci --cache .npm --prefer-offline
   before_script: &npm
     - rm -rvf /etc/apt/sources.list /etc/apt/sources.list.d
     - install -v -T -m 0644 ${APT_SOURCES_LIST} /etc/apt/sources.list