Disable gzip on HEAD requests in v2 endpoints

nginx's gzip module will ignore the content-length header on the HEAD request and try to gzip the body.... but there is no body, so it simply writes no header at all.

Code to turn this off was based off of https://trac.nginx.org/nginx/ticket/261

conf/nginx/server-base.conf.jnj

@@ -105,6 +105,10 @@ location ~ ^/v2 {
         return 404;
     }
 
+    if ($request_method = HEAD ) {
+        gzip off;
+    }
+
     # Setting ANY header clears all inherited proxy_set_header directives
     proxy_set_header X-Forwarded-For $proper_forwarded_for;
     proxy_set_header X-Forwarded-Proto $proper_scheme;