gitlab-ci for nuxt 2.15

I had to change the gitlab-ci file, nuxt generate fails because it can't find some node_modules. This means that something is off with the "before_script" instruction of the gitlab-ci.yml

By looking at nuxt official documentation for docker, the first step is:

yarn install --prefer-offline --frozen-lockfile --non-interactive --production=false

and not

npm install

with this change the job ends in success, maybe this will help someone, cheers