[minor] Debug the response headers.

Author: indexzero

index.js

@@ -660,6 +660,8 @@ Mana.prototype.send = function send(args) {
        * @api private
        */
       function parse(err, res, body) {
+        mana.debug('Response headers %j', res.headers || {});
+
         if (err) {
           mana.debug('Received an error (%s) for URL %s', err.message, options.uri);