Update contributions.adoc

Fixed broken image link shaderblow.

src/docs/asciidoc/jme3/contributions.adoc

@@ -111,7 +111,7 @@ a| Yes
 The “Shaderblow library contains various shader effects, e.g. refraction, particles, forceshields, grayscale and much more.
 
 
-image::http://jmonkeyengine.org/wiki/lib/exe/fetch.php/sdk:plugin:glass-shader.png[glass-shader.png,width="150",height="",align="right"]
+image::sdk/plugin/glass-shader.png[glass-shader.png,width="150",height="",align="right"]
 
 [cols="2", options="header"]
 |===