Upgrade Nuxt

Upgrade the Nuxt version from 2.12.0 to 2.14.0.

To install the latest version, run npm install --save-dev.

There is one incompability with a setting in the nuxt.config.js file made by Martin:

  router: {
    base: process.env.BASE_URL || '/'
  }

This router setting had to be removed as it appends the BASE_URL to the already existing BASE_URL. I think the BASE_URL is now used to define the path after the URL, not the whole URL itself.