Merge pull request #23889 from sdurrheimer/zsh-completion-storage-driver-overlay2

Add zsh completion for 'docker daemon --storage-driver (overlay2|vfs)'

contrib/completion/zsh/_docker

@@ -974,7 +974,7 @@ __docker_subcommand() {
                 "($help -p --pidfile)"{-p=,--pidfile=}"[Path to use for daemon PID file]:PID file:_files" \
                 "($help)--raw-logs[Full timestamps without ANSI coloring]" \
                 "($help)*--registry-mirror=[Preferred Docker registry mirror]:registry mirror: " \
-                "($help -s --storage-driver)"{-s=,--storage-driver=}"[Storage driver to use]:driver:(aufs devicemapper btrfs zfs overlay)" \
+                "($help -s --storage-driver)"{-s=,--storage-driver=}"[Storage driver to use]:driver:(aufs btrfs devicemapper overlay overlay2 vfs zfs)" \
                 "($help)--selinux-enabled[Enable selinux support]" \
                 "($help)*--storage-opt=[Storage driver options]:storage driver options: " \
                 "($help)--tls[Use TLS]" \