Bugfix: NULL not declared

Former-commit-id: 99c7d00b99e55827643152823e334b011a0ef488

include/igl/Timer.h

@@ -21,6 +21,7 @@
 #else
 #include <sys/time.h>
 #endif
+#include <cstddef>
 
 namespace igl
 {