fix: correct the name of C++ (doocs#872)

hdgaadd · web-flow · commit 5d6338cd0ebc · 2022-11-01T21:49:50.000+08:00
diff --git a/solution/2400-2499/2455.Average Value of Even Numbers That Are Divisible by Three/README.md b/solution/2400-2499/2455.Average Value of Even Numbers That Are Divisible by Three/README.md
@@ -83,7 +83,7 @@ class Solution {
 }
 ```
 
-### **C+++**
+### **C++**
 
 ```cpp
 class Solution {
