Fix Node regression

[mramato]

I introduced a bug in #7514 where Resource was broken from inside of Node.js because the built version of cesium was using a different globally defined require than Node's require. One of these days we'll have full Node testing, but this is one of the fuzzy parts of the API that we don't normally ever use via Node.

To test this, first run minifyRelease then run NODE_ENV=production node and paste the below code into the interpreter:

const Cesium = require('./index.js');
Cesium.IonResource.fromAssetId(1);

You should see { then: [Function: e] } as output. Previously it would crash with a No url error and callstack.

[cesium-concierge]

Thanks for the pull request @mramato!

• ✔️ Signed CLA found.
• ❔ Unit tests were not updated.
  • Make sure you've updated tests to reflect your changes, added tests for any new code, and ran the code coverage tool.

Reviewers, don't forget to make sure that:

• Cesium Viewer works.
• Works in 2D/CV.
• Works (or fails gracefully) in IE11.

[hpinkos]

Thanks @mramato