Fixed bug in category command

libCore.js

@@ -287,10 +287,10 @@ exports.getQuotes = async function (quote_url) {
  * getCategories - Returns feed categories
  * @constructor
  */
-exports.getCategories = function () {
+exports.getCategories = async (callback) => {
   feedStorage.getUniqueByKey("category", (err, results) => {
-    if (err) throw err;
+    if (err) return callback(err, undefined);
     
-    return results
+    return callback(undefined, results);    
   });
 }