Fix autocompletion of Docker containers

Since version 0.6.5, Docker ensures that new containers are named by generating it if not passed.
This commit fixes the container autocompletion by referring to the last column given by `docker ps -a`.

plugins/docker/_docker

@@ -10,7 +10,7 @@
 # Output a selectable list of all running docker containers
 __docker_containers() {
     declare -a cont_cmd
-    cont_cmd=($(docker ps | awk 'NR>1{print $1":[CON("$1")"$2"("$3")]"}'))
+    cont_cmd=($(docker ps -a | awk 'NR>1{print $NF}'))
     _describe 'containers' cont_cmd
 }