fix memory leak

Author: stevengj

src/GDSIIgeom.cpp

@@ -153,6 +153,7 @@ geometric_object_list get_GDSII_prisms(material_type material, const char *GDSII
     double height = zmax - zmin;
     vector3 zaxis = {0, 0, 1};
     prisms.items[np] = make_prism(material, vertices, num_vertices, height, zaxis);
+    delete[] vertices; // make_prism copies the data
   }
   return prisms;
 }