----
so you're going to need to also add a new volume for special directives for old clients. you need to follow these instructions, and then start a new nginx-proxy container with a new volume:
-v /var/docker/nginx-proxy/vhost.d:/etc/nginx/vhost.d:ro

but first you need to do this:
sudo mkdir -p /var/docker/nginx-proxy/vhost.d && cd /var/docker/nginx-proxy
sudo vim vhost.d/myregistry.example.com
add the following:
----

client_max_body_size 0;
chunked_transfer_encoding on;

location /v2/ {
  # Do not allow connections from docker 1.5 and earlier
  # docker pre-1.6.0 did not properly set the user agent on ping, catch "Go *" user agents
  if ($http_user_agent ~ "^(docker\/1\.(3|4|5(?!\.[0-9]-dev))|Go ).*$" ) {
    return 404;
  }

  add_header Docker-Distribution-Api-Version "registry/2.0";
  #more_set_headers     'Content-Type: application/json; charset=utf-8';
  include               vhost.d/docker-registry.conf;
}

location /v1/_ping {
  auth_basic off;
  include               vhost.d/docker-registry.conf;
  add_header X-Ping     "inside /v1/_ping";
  add_header X-Ping     "INSIDE /v1/_ping";
}

location /v1/users {
  auth_basic off;
  include               vhost.d/docker-registry.conf;
  add_header X-Users    "inside /v1/users";
  add_header X-Users    "INSIDE /v1/users";
}

=================== THEN create a file: sudo vim /var/docker/nginx-proxy/vhost.d/docker-registry.conf

proxy_pass                          http://myregistry.mexample.com;
proxy_set_header  Host              $http_host;   # required for docker client's sake
proxy_set_header  X-Real-IP         $remote_addr; # pass on real client's IP
proxy_set_header  X-Forwarded-For   $proxy_add_x_forwarded_for;
proxy_set_header  X-Forwarded-Proto $scheme;
proxy_read_timeout                  900;