Change forum links to users to use attributes from header

docs/modules/contributions/pages/contributions.adoc

@@ -154,7 +154,7 @@ A fairly complete set of painting tools for editing jME3 Images from code.
 |===
 
 a| *Contact person*
-a| link:https://hub.jmonkeyengine.org/users/zarch/activity[zarch]
+a| {url-forum-user}/zarch/activity[zarch]
 
 a| *Documentation*
 a| link:https://hub.jmonkeyengine.org/t/image-painter-plugin-available/24255[Forum Post, full javadoc in plugin]
@@ -178,7 +178,7 @@ Next Generation Particle Emitters.
 |===
 
 a| *Contact person*
-a| link:https://hub.jmonkeyengine.org/users/zarch/activity[zarch]
+a| {url-forum-user}/zarch/activity[zarch]
 
 a| *Documentation*
 a| xref:effect/particles/particles.adoc[Wiki Page]