Add zsh completion for 'docker daemon --authz-plugin'

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

contrib/completion/zsh/_docker

@@ -578,6 +578,7 @@ __docker_subcommand() {
             _arguments $(__docker_arguments) \
                 $opts_help \
                 "($help)--api-cors-header=[Set CORS headers in the remote API]:CORS headers: " \
+                "($help)*--authz-plugin=[Set authorization plugins to load]" \
                 "($help -b --bridge)"{-b=,--bridge=}"[Attach containers to a network bridge]:bridge:_net_interfaces" \
                 "($help)--bip=[Specify network bridge IP]" \
                 "($help -D --debug)"{-D,--debug}"[Enable debug mode]" \