Fix moment-import.html causing 404 in Nuxeo Elements tutorial

nuxeo-ui-elements/moment-import.html has a line referencing '../moment/moment-with-locales.min.js'. When ran in the context of the Customize Your App with Nuxeo Elements tutorial for LTS 2019, this causes a 404 as the path should start with '../bower_components'.

Steps to Reproduce:

1. Follow the nuxeo-elements-tutorial for LTS 2019 up through the Add UI Elements section
2. Open the running Polymer app and observe the browser dev tools console

Expected behavior: no errors visible

Actual behavior: 404 error seen on attempting to import moment-with-locales.min.js