fix bug

Author: lrvideckis

library/data_structures/dsu/kruskal_tree.hpp

@@ -5,7 +5,7 @@
 struct kr_tree {
   int id;
   vi p;
-  vector<array<int, 2>> adj;
+  vector<vi> adj;
   kr_tree(int n): id(n), p(2 * n, -1), adj(2 * n) {}
   int find(int v) {
     return p[v] < 0 ? v : p[v] = find(p[v]);