Log HTTP server errors

Summary: Currently, we are not interested in these errors. Let's add some logging as a way of knowing if they take place and why.

Reviewed By: antonk52

Differential Revision: D49828378

fbshipit-source-id: f741a45e1ba9892aa54dca85f97bcc419e0b5e25

desktop/flipper-server-core/src/server/startServer.tsx

@@ -164,6 +164,10 @@ async function startHTTPServer(
     server.close();
   });
 
+  server.on('error', (e: Error) => {
+    console.warn('[flipper-server] HTTP server error: ', e);
+  });
+
   server.listen(config.port);
 
   /**