Tighten check for Moment

[jonrimmer]

This slightly tightens the check for Moment. This is so you can use the browser field to exclude Moment from the bundle (as per #5978). By default, ignoring a module makes it return an empty object, and this was passing the check.

[simonbrunel]

Just tested with this project reported in this comment (@lsn793) and it works as expected with:

// package.json
{
  "browser": {
    "moment": false
  }
}

Thanks @jonrimmer for this find.

I also noticed that this project includes chartjs-plugin-annotation which had chart.js as dependency (instead of peer dependency). The consequence is that Chart.js is included two times in the built file. And it's currently the same with the zoom plugin (until 0.7.0, not released yet).

Angular projects using the zoom and annotation plugins will get the source of Chart.js included 3 times in the built file (I didn't try with Webpack projects). I don't understand why this hasn't been already reported.