fix(electron): ipfs proxy should have error status code

electron/proxy-server.js

@@ -23,7 +23,9 @@ proxy.on('proxyReq', function (proxyReq, req, res, options) {
 proxy.on('error', (e, req, res) => {
   console.error(e);
   // if not ended, will hang forever
-  res.end();
+  res.statusCode = 502;
+  res.setHeader('Content-Type', 'text/plain');
+  res.end(`502 Bad Gateway: ${e.message}`);
 });
 
 // start server