Missing include.

Former-commit-id: 6dc5c11965d3610b366ae55147e36b11fc47501a

include/igl/copyleft/cgal/SelfIntersectMesh.h

@@ -10,6 +10,7 @@
 
 #include "CGAL_includes.hpp"
 #include "RemeshSelfIntersectionsParam.h"
+#include "../../unique.h"
 
 #include <Eigen/Dense>
 #include <list>