change to xref

docs/modules/tutorials/pages/beginner/solutions.adoc

@@ -4,7 +4,7 @@
 :revdate: 2020/07/06
 
 
-This is a user-proposed group of solutions for some or all of the exercises presented throughout the beginner tutorials (<<jme3#tutorials_for_beginners#,jme3#tutorials_for_beginners>>).
+This is a user-proposed group of solutions for some or all of the exercises presented throughout the beginner tutorials (xref:ROOT:jme3.adoc#tutorials_for_beginners[tutorials_for_beginners]).
 There are several ways to do them, so take what you see with a grain of salt, and actually try to do them yourself instead of jumping to the solution, for it is the best way to learn!