fix vmod object constructor documentation
fix vmod object constructor documentation

The vmod name got lost in e7c0497404a5b4aadda71aead3b0e7fe946d6993

example before/after diff:

- new xshard_param = shard_param()
+ new xshard_param = directors.shard_param()

gquintard/Varnish-Cache,gquintard/Varnish-Cache,gquintard/Varnish-Cache,gquintard/Varnish-Cache