webpack-dev-server patch for 'still-ok' success status (facebook#1377)

Author: Robbie H

packages/react-dev-utils/webpackHotDevClient.js

@@ -248,6 +248,7 @@ connection.onmessage = function(e) {
   case 'hash':
     handleAvailableHash(message.data);
     break;
+  case 'still-ok':
   case 'ok':
     handleSuccess();
     break;