Solved compilation error

Renamed the variable "st" to loop over at line 21.

Author: caba5

cpp/953-Alien-Dictionary.cpp

@@ -18,7 +18,7 @@ class Solution {
 
         // indegree make all char 0
         for(auto word : words){
-            for(auto c : st){
+            for(auto c : word){
                 indegree[c]=0;
             }
         }