Increasing server names hash size

[stuartpb]

Dokku has a line that effectively does this:

echo "server_names_hash_bucket_size 64;" \
  > "$PLUSHU_ROOT/nginx.conf.d/name-hash-size.conf"

http://nginx.org/en/docs/http/server_names.html describes why you would want to increase the server_names_hash_bucket_size or server_names_hash_max_size. However, server_names_hash_bucket_size is supposed to based on properties of the CPU by default (and it could even be set to 128, from what I can read of the documentation), and would only need to be expanded in certain configurations.

As such, I think this change should best be left as an option for installations to opt into manually on a case-by-case basis.