Fixing "fall_protection" options

missilewars-plugin/src/main/java/de/butzlabben/missilewars/configuration/arena/FallProtectionConfiguration.java

@@ -28,7 +28,7 @@ import lombok.ToString;
 @RequiredArgsConstructor
 public class FallProtectionConfiguration {
 
-    private final boolean enabled = true;
-    private final int duration = 60;
+    private boolean enabled = true;
+    private int duration = 60;
     @SerializedName("message_only_on_start") private boolean messageOnlyOnStart = false;
 }