fixup: update error message expectation

Author: JakobJingleheimer

test/parallel/test-assert-async.js

@@ -103,8 +103,9 @@ const invalidThenableFunc = () => {
   promises.push(assert.rejects(promise, {
     name: 'TypeError',
     code: 'ERR_INVALID_RETURN_VALUE',
+    // FIXME: This should use substring matching for key words, like /Promise/ and /undefined/
     message: 'Expected instance of Promise to be returned ' +
-             'from the "promiseFn" function but got type undefined.'
+             'from the "promiseFn" function but got undefined.'
   }));
 
   promise = assert.rejects(Promise.resolve(), common.mustNotCall());