Update global_constants.cpp

Making KEY_MASK_CMD usable in GDScript

core/global_constants.cpp

@@ -313,6 +313,7 @@ static _GlobalConstant _global_constants[]={
 	BIND_GLOBAL_CONSTANT( KEY_MASK_ALT   ),
 	BIND_GLOBAL_CONSTANT( KEY_MASK_META   ),
 	BIND_GLOBAL_CONSTANT( KEY_MASK_CTRL   ),
+	BIND_GLOBAL_CONSTANT( KEY_MASK_CMD   ),
 	BIND_GLOBAL_CONSTANT( KEY_MASK_KPAD   ),
 	BIND_GLOBAL_CONSTANT( KEY_MASK_GROUP_SWITCH   ),