point link to attachment

docs/modules/core/pages/gui/nifty_gui.adoc

@@ -64,7 +64,7 @@ Nifty GUIs are made up of the following *elements*:
 **  link:https://github.com/jMonkeyEngine/jmonkeyengine/blob/master/jme3-examples/src/main/java/jme3test/niftygui/TestNiftyToMesh.java[TestNiftyToMesh.java] - Can be found in <<sdk:sample_code.adoc#the-jme3tests-project-template,jme3 tests>> also.
 
 *  jME3-ready version of the Nifty +++<abbr title="Graphical User Interface">GUI</abbr>+++ 1.3 demo (sample code, Java)
-**  link:http://files.seapegasus.org/NiftyGuiDemo.zip[NiftyGuiDemo.zip]
+**  link:{attachmentsdir}/NiftyGuiDemo.zip[NiftyGuiDemo.zip]
 
 *  Find more sample code in the link:https://github.com/nifty-gui/nifty-gui/tree/1.4/nifty-examples/src/main/java/de/lessvoid/nifty/examples[nifty-examples] repositories.
 **  link:https://github.com/nifty-gui/nifty-gui/wiki/Examples[Running The Nifty Examples]