nginx config: chunked_transfer_encoding and proxy_read_timeout

Had some trouble pushing images.  Adding these settings based on
<https://github.com/docker/docker-registry/blob/master/contrib/nginx_1-3-9.conf>
resolved the problem.
Update to work with latest `registry` repo from Docker
Merge pull request #9 from manny-fp/master

Update to work with latest `registry` repo from Docker