Update free_skymaps.adoc

Minor tweak to note.

src/docs/asciidoc/jme3/advanced/free_skymaps.adoc

@@ -19,7 +19,7 @@ Using Blender you can create your skymaps for free. Once link:https://www.blende
 ====
 This tutorial is an adaptation of contributor glaucomardanos production, not an exact duplicate. +
 These steps assume you're using the default blender setup and apply to vers 2.78c+. +
-This is in checklist format so you can mark items as you go to keep your place.
+The tutorial is in checklist format so you can mark items as you go to keep your place.
 ====
 
 [%interactive]