Add zsh completion for 'unless-stopped' restart policy

Signed-off-by: Steve Durrheimer <s.durrheimer@gmail.com>

contrib/completion/zsh/_docker

@@ -438,7 +438,7 @@ __docker_subcommand() {
         "($help)--pid=-[PID namespace to use]:PID: "
         "($help)--privileged[Give extended privileges to this container]"
         "($help)--read-only[Mount the container's root filesystem as read only]"
-        "($help)--restart=-[Restart policy]:restart policy:(no on-failure always)"
+        "($help)--restart=-[Restart policy]:restart policy:(no on-failure always unless-stopped)"
         "($help)*--security-opt=-[Security options]:security option: "
         "($help -t --tty)"{-t,--tty}"[Allocate a pseudo-tty]"
         "($help -u --user)"{-u,--user=-}"[Username or UID]:user:_users"