Use versions file from elastic/docs for install-upgrade guide (elastic#512)

Author: jrodewig

docs/en/install-upgrade/index.asciidoc

@@ -3,8 +3,8 @@
 :es-repo-dir:        {docdir}/../../../../elasticsearch/docs
 :kib-repo-dir:       {docdir}/../../../../kibana/docs
 
+include::{asciidoc-dir}/../../shared/versions/stack/{source_branch}.asciidoc[]
 include::{asciidoc-dir}/../../shared/attributes.asciidoc[]
-include::{es-repo-dir}/Versions.asciidoc[]
 
 [[elastic-stack]]
 == Overview