missing include

Former-commit-id: bee828aa539f17a3deb7c75b216899b668ed1646

include/igl/ray_box_intersect.cpp

@@ -1,4 +1,6 @@
 #include "ray_box_intersect.h"
+#include <vector>
+
 template <
   typename Derivedsource,
   typename Deriveddir,