Popup flows that do not return id_token break

[rolodato]

The following cases return a false positive error when using popup mode on latest auth0.js 7:

• response_type=token without any scope (need to explicitly pass scope: '')
• response_type=token with an audience parameter

In both of these cases, there is only an access_token returned, which returns an error after this check:

auth0.js/index.js

Lines 972 to 974 in dbe1663

	if (result.id_token) {
	return callback(null, _this._prepareResult(result));
	}