fix: Error codes are not shown in the response

backend/package.json

@@ -1,6 +1,6 @@
 {
   "name": "sub-store",
-  "version": "2.8.4",
+  "version": "2.8.5",
   "description": "Advanced Subscription Manager for QX, Loon, Surge, Stash and ShadowRocket.",
   "main": "src/main.js",
   "scripts": {

backend/src/restful/errors/index.js

@@ -1,5 +1,6 @@
 class BaseError {
     constructor(code, message, details) {
+        this.code = code;
         this.message = message;
         this.details = details;
     }