Add a "Mountain" type to the ViewElement enumeration.

src/main/java/view/ViewElement.java

@@ -3,7 +3,7 @@ package view;
 import javafx.scene.paint.Color;
 
 public enum ViewElement {
-  FIREFIGHTER(Color.BLUE), FIRE(Color.RED), EMPTY(Color.WHITE) ,  CLOUD(Color.GRAY);;
+  FIREFIGHTER(Color.BLUE), FIRE(Color.RED), EMPTY(Color.WHITE) ,  CLOUD(Color.GRAY),     MOUNTAIN(Color.GRAY);
   final Color color;
   ViewElement(Color color) {
     this.color = color;