[fix] Dont force `Connection: close` now that Keep-Alive is supported

lib/node-http-proxy.js

@@ -412,10 +412,6 @@ HttpProxy.prototype.proxyRequest = function (req, res, options) {
     path: req.url,
     headers: req.headers
   };
-    
-  // Force the `connection` header to be 'close' until
-  // node.js core re-implements 'keep-alive'.
-  outgoing.headers['connection'] = 'close';
   
   protocol = _getProtocol(options.https || this.target.https, outgoing);