Update 8.18 asciidoc

Author: alaudazzi

shared/versions/stack/8.18.asciidoc

@@ -29,7 +29,7 @@ release-state can be: released | prerelease | unreleased
 //////////
 is-current-version can be: true | false
 //////////
-:is-current-version:    true
+:is-current-version:    false
 
 //////////
 hide-xpack-tags defaults to "false" (they are shown unless set to "true")