Merge pull request #25458 from sfsmithcha/fix_swarm_update_typo

fix typo, change sample cert expiry value
(cherry picked from commit e62b9450136595ac73b4fd0de766d072c1a6954a)

Signed-off-by: Sven Dowideit <SvenDowideit@home.org.au>
(cherry picked from commit f72a1eb6bed1684bb3f282227ae761c6e0532714)
Signed-off-by: Tibor Vass <tibor@docker.com>

docs/reference/commandline/swarm_update.md

@@ -29,7 +29,7 @@ Updates a swarm cluster with new parameter values. This command must target a ma
 
 
 ```bash
-$ docker swarm update --cert-expirty 4000h0m0s
+$ docker swarm update --cert-expiry 720h
 ```
 
 ## Related information