Fix DemoGUI bug

Author: Mgazul

src/main/java/com/mohistmc/api/gui/DemoGUI.java

@@ -6,6 +6,7 @@
 import org.bukkit.Material;
 import org.bukkit.entity.Player;
 import org.bukkit.event.inventory.ClickType;
+import org.bukkit.event.inventory.InventoryCloseEvent;
 import org.bukkit.inventory.ItemStack;
 
 public class DemoGUI {
@@ -32,7 +33,9 @@ public DemoGUI(String name) {
                 .toItemStack()) {
             @Override
             public void ClickAction(ClickType type, Player u, ItemStack itemStack) {
-                u.closeInventory();
+                if (!type.isShiftClick() && type.isLeftClick()) {
+                    u.closeInventory();
+                }
             }
         });
     }