add default return value to Two-Sum solution

0001-Two-Sum/Article/0001-Two-Sum.md

@@ -57,6 +57,7 @@ public:
 
             record[nums[i]] = i;
         }
+        return {};
     }
 };
 
@@ -66,4 +67,4 @@ public:
 
 
 
-![](../../Pictures/qrcode.jpg)
\ No newline at end of file
+![](../../Pictures/qrcode.jpg)