[DOCS] Adds missing anchor in Installation Upgrade Guide (#223)

Author: lcawl

docs/en/install-upgrade/index.asciidoc

@@ -1,4 +1,3 @@
-[[elastic-stack]]
 = Elastic Stack
 
 :es-repo-dir:        {docdir}/../../../../elasticsearch/docs
@@ -7,6 +6,7 @@
 include::{asciidoc-dir}/../../shared/attributes62.asciidoc[]
 include::{es-repo-dir}/Versions.asciidoc[]
 
+[[elastic-stack]]
 == Overview
 
 The products in the https://www.elastic.co/products[Elastic Stack]