Add missing header for std::tolower (#4156)

* Add missing header for std::tolower

Missing header causes syntax error when compiling for Windows using Visual studio 2017. Closes #4155

* Reordered STL header includes in order to pass style check

ngraph/core/src/op/util/attr_types.cpp

@@ -13,6 +13,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 //*****************************************************************************
+#include <cctype>
 #include <map>
 
 #include "ngraph/attribute_visitor.hpp"