Fix incorrect property name in test/main.ts

Author: poiru

test-smoke/electron/test/main.ts

@@ -829,7 +829,7 @@ app.on("ready", () => {
   });
 
   protocol.registerBufferProtocol("atom", (request, callback) => {
-    callback({ mimeType: "text/html", buffer: new Buffer("<h5>Response</h5>") });
+    callback({ mimeType: "text/html", data: new Buffer("<h5>Response</h5>") });
   });
 
   protocol.registerStringProtocol("atom", (request, callback) => {