Fix deprecation warning about cylc-ui HOT 3 CLOSED

> [email protected] lint /home/kinow/Development/python/workspace/cylc-web
> vue-cli-service lint

error: The "Footer" component has been registered but not used (vue/no-unused-components) at src/layouts/Default.vue:28:5:
  26 |     Toolbar,
  27 |     Drawer,
> 28 |     Footer
     |     ^
  29 |   }
  30 | }
  31 | </script>


1 error found.
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! [email protected] lint: `vue-cli-service lint`
npm ERR! Exit status 1
npm ERR! 
npm ERR! Failed at the [email protected] lint script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR!     /home/kinow/.npm/_logs/2019-02-11T09_45_45_485Z-debug.log