I edtited node_helper.js in this folder MagicMirror/js and could not find the code you asked me to change. The only reference I found that checking the response return code 200 is
NodeHelper.checkFetchStatus = function (response) {
// response.status >= 200 && response.status < 300
if (response.ok) {
return response;
} else {
throw Error(response.statusText);
}
};