Improve bash completion for `create|run --stop-signal`

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

contrib/completion/bash/docker

@@ -1704,6 +1704,10 @@ _docker_container_run_and_create() {
 			fi
 			return
 			;;
+		--stop-signal)
+			__docker_complete_signals
+			return
+			;;
 		--storage-opt)
 			COMPREPLY=( $( compgen -W "size" -S = -- "$cur") )
 			__docker_nospace