Add import assertion (now required by node@16)

This should fix the breaking CI test.   Apparently node@16 now throws if you try to import a .json file with no import assertion.
Ref: nodejs/node#40250

cc: @ctavan  for sanity check to make sure this won't break anything.

examples/node-esmodules/example.mjs

@@ -10,7 +10,7 @@ import {
   version as uuidVersion,
 } from 'uuid';
 import * as uuid from 'uuid';
-import pkg from 'uuid/package.json';
+import pkg from 'uuid/package.json' assert {type: 'json'};
 
 console.log('uuidv1()', uuidv1());