Refactor: remove random char

app/Controllers/AdminController.php

@@ -117,7 +117,7 @@ class AdminController extends UserController
         $code = new Coupon();
         $code->onetime=$request->getParam('onetime');
 
-        $code->code=$request->getParam('prefix').Tools::genRandomChar(8);
+        $code->code = $request->getParam('prefix');
         $code->expire=time()+$request->getParam('expire')*3600;
         $code->shop=$request->getParam('shop');
         $code->credit=$request->getParam('credit');