docs: update api examples (#3788)

Author: snitin315

examples/api/middleware/server.js

@@ -8,6 +8,6 @@ const compiler = Webpack(webpackConfig);
 const devServerOptions = webpackConfig.devServer;
 const server = new WebpackDevServer(devServerOptions, compiler);
 
-server.listen(8080, "127.0.0.1", () => {
+server.startCallback(() => {
   console.log("Starting server on http://localhost:8080");
 });

examples/api/simple/server.js

@@ -8,6 +8,6 @@ const compiler = Webpack(webpackConfig);
 const devServerOptions = { ...webpackConfig.devServer, open: true };
 const server = new WebpackDevServer(devServerOptions, compiler);
 
-server.listen(8080, "127.0.0.1", () => {
+server.startCallback(() => {
   console.log("Starting server on http://localhost:8080");
 });