fixed relative attribute

src/docs/asciidoc/jme3/external/blender/blender_gltf.adoc

@@ -1,6 +1,6 @@
 = Exporting Models as GlTF meshes from Blender
 :revnumber: 2.0
-:relfileprefix: ../../
+:relfileprefix: ../../../
 :imagesdir: ../..
 ifdef::env-github,env-browser[:outfilesuffix: .adoc]