Remove agent:false to allow globalAgent use

Author: brycekahle

lib/transport/driver/xhr.js

@@ -24,7 +24,6 @@ function XhrDriver(method, url, payload, opts) {
   , port: parsedUrl.port
   , path: parsedUrl.pathname + (parsedUrl.query || '')
   , headers: opts && opts.headers
-  , agent: false
   };
 
   var protocol = parsedUrl.protocol === 'https:' ? https : http;