Test fails because it doesn't find the Cypress binary

I tried the sample gitlab-ci file with a blank project, and I got the following error :

$ $(npm bin)/cypress run
The cypress npm package is installed, but the Cypress binary is missing.

We expected the binary to be installed here: /builds/cypress-io/cypress-example-docker-gitlab/cache/Cypress/3.3.1/Cypress/Cypress

Reasons it may be missing:

- You're caching 'node_modules' but are not caching this path: /root/.cache/Cypress
- You ran 'npm install' at an earlier build step but did not persist: /root/.cache/Cypress

Properly caching the binary will fix this error and avoid downloading and unzipping Cypress.

Alternatively, you can run 'cypress install' to download the binary again.

https://on.cypress.io/not-installed-ci-error

Do you have an idea what did I do wrong ?