Add bash completion for `update --cpus`

Signed-off-by: Harald Albers <github@albersweb.de>

contrib/completion/bash/docker

@@ -1845,6 +1845,7 @@ _docker_container_update() {
 		--cpu-quota
 		--cpu-rt-period
 		--cpu-rt-runtime
+		--cpus
 		--cpuset-cpus
 		--cpuset-mems
 		--cpu-shares -c