Install Node packages before compiling assets in Gitlab CI

The asset compilation was failing because it needs the packages that are
installed with `npm clean-install`.

We're now installing the Node packages after installing the gems, like
we do in Github Actions. For this, we need to install the `npm` package.

.gitlab-ci.yml

@@ -17,13 +17,13 @@ tests:
     TEST_COVERAGE: 1
   parallel: 5
   script:
-    - apt-get update && apt-get install -y nodejs chromium
+    - apt-get update && apt-get install -y nodejs npm chromium
     - for i in config/*.example; do cp "$i" "${i/.example}"; done
     - for i in config/*.gitlab; do cp "$i" "${i/.gitlab}"; done
     - bundle --without development
+    - npm clean-install
     - bundle exec rake db:setup
     - bundle exec rake assets:precompile > /dev/null 2>&1
-    - npm clean-install
     - bin/knapsack_pro_rspec
   artifacts:
     when: on_failure