nav.adoc: correct broken xref in nav

docs/modules/contributions/nav.adoc

@@ -1,5 +1,5 @@
 * User Contributions
-** xref:docs\modules\contributions\pages\contributions.adoc[User Made Utilities]
+** xref:contributions.adoc[User Made Utilities]
 ** Shader
 *** xref:shader/shaderblow_project.adoc[ShaderBlow Project]
 ** Landscapes