add include for MandatoryValidator

Author: Glass

Framework/Algorithms/src/Divide.cpp

@@ -5,6 +5,7 @@
 //   Institut Laue - Langevin & CSNS, Institute of High Energy Physics, CAS
 // SPDX - License - Identifier: GPL - 3.0 +
 #include "MantidAlgorithms/Divide.h"
+#include "MantidKernel/MandatoryValidator.h"
 
 using namespace Mantid::API;
 using namespace Mantid::Kernel;