Remove redundant "after"

Author: freakingid

docs/upgrading-stack.asciidoc

@@ -235,7 +235,7 @@ index as alias for the new index and delete the 2.x index.
 The format used for the internal indices used by Kibana and {xpack} has
 changed in {major-version}. Before you can run Kibana and {xpack} in {version},
 these indices must be upgraded to the new format. If you are upgrading from a
-version prior to 5.6, you must upgrade them after after installing
+version prior to 5.6, you must upgrade them after installing
 Elasticsearch {version}.
 
 To get a list of the indices that need to be upgraded, install {xpack} and use