docs: fix description of `docker swarm update --help`

Signed-off-by: Kei Ohmura <ohmura.kei@gmail.com>
(cherry picked from commit 2f0e00f58723cb3e063b49f564173b3768476c99)
Signed-off-by: Victor Vieux <vieux@docker.com>

docs/reference/commandline/swarm_update.md

@@ -24,10 +24,10 @@ Options:
       --autolock                        Change manager autolocking setting (true|false)
       --cert-expiry duration            Validity period for node certificates (ns|us|ms|s|m|h) (default 2160h0m0s)
       --dispatcher-heartbeat duration   Dispatcher heartbeat period (ns|us|ms|s|m|h) (default 5s)
-      --external-ca value               Specifications of one or more certificate signing endpoints
+      --external-ca external-ca         Specifications of one or more certificate signing endpoints
       --help                            Print usage
-      --max-snapshots int               Number of additional Raft snapshots to retain
-      --snapshot-interval int           Number of log entries between Raft snapshots
+      --max-snapshots uint              Number of additional Raft snapshots to retain
+      --snapshot-interval uint          Number of log entries between Raft snapshots (default 10000)
       --task-history-limit int          Task history retention limit (default 5)
 ```