missing includes

Former-commit-id: 836b2ea5c06ee5a1c91a13c756a0bfc5500e5b38

include/igl/copyleft/cgal/extract_cells.cpp

@@ -19,6 +19,8 @@
 #include <iostream>
 #include <vector>
 #include <queue>
+#include <map>
+#include <set>
 
 //#define EXTRACT_CELLS_DEBUG