fix.

Former-commit-id: eccf57327d810374ad30d0645f4f89a02c6b4d97

include/igl/copyleft/cgal/wire_mesh.cpp

@@ -2,6 +2,7 @@
 
 #include "../../list_to_matrix.h"
 #include "../../slice.h"
+#include "../../PI.h"
 #include "convex_hull.h"
 #include "mesh_boolean.h"
 #include <Eigen/Geometry>