fix: code block label

No.0056.Merge Intervals

Author: YangFong

solution/0000-0099/0056.Merge Intervals/README.md

@@ -222,7 +222,7 @@ func max(a, b int) int {
 
 ### **C#**
 
-```cpp
+```cs
 public class Solution {
     public int[][] Merge(int[][] intervals) {
         var res = new List<int[]>();

solution/0000-0099/0056.Merge Intervals/README_EN.md

@@ -192,7 +192,7 @@ func max(a, b int) int {
 
 ### **C#**
 
-```cpp
+```cs
 public class Solution {
     public int[][] Merge(int[][] intervals) {
         var res = new List<int[]>();