Fix xmlhttprequest example

The "pressed" property belongs to mouseArea, not button.

Change-Id: Ib35c520b75e30c2cb9a3a7dee0b482a2209040c8
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

examples/qml/xmlhttprequest/Get.qml

@@ -58,7 +58,7 @@ GetForm
 
     mouseArea.onClicked: Utils.makeRequest()
 
-    button.border.width: button.pressed ? 2 : 1
+    button.border.width: mouseArea.pressed ? 2 : 1
     text.text: "Request data.xml"
 
 }