fix link

docs/modules/core/pages/util/sky.adoc

@@ -53,5 +53,5 @@ Box or Sphere?
 
 For more information on Skymap creation see:
 
-*  xref:xref:tutorials:how-to/util/free_skymaps.adoc[How to create free skymaps]
+*  xref:tutorials:how-to/util/free_skymaps.adoc[How to create free skymaps]
 *  <<tutorials:how-to/modeling/blender/blender.adoc#skybox-baking,SkyBox baking>>