Replaced Object.keys().map with for in loop.

Author: ArGGu

Diff for: lib/http-proxy/passes/ws-incoming.js

@@ -118,7 +118,7 @@ var passes = exports;
         'HTTP/1.1 101 Switching Protocols'
       ];
 
-      Object.keys(proxyRes.headers).map(function(i) {
+      for(var i in proxyRes.headers) {
           if (util.isArray(proxyRes.headers[i])) {
             var a   = proxyRes.headers[i];
             var len = a.length;
@@ -129,7 +129,7 @@ var passes = exports;
         } else {
           writeHead.push(i + ": " + proxyRes.headers[i]);
         }
-      });
+      }
 
       socket.write(writeHead.join('\r\n') + '\r\n\r\n');
       proxySocket.pipe(socket).pipe(proxySocket);