Do not await the browser to close (GoogleCloudPlatform#653)

Awaiting for the headless browser to be closed add a certain amount of time to the duration of the request, although the image is already ready to be sent back to the user.

Author: glaforge

appengine/headless-chrome/app.js

@@ -35,7 +35,7 @@ app.use(async (req, res) => {
  const page = await browser.newPage();
  await page.goto(url);
  const imageBuffer = await page.screenshot();
- await browser.close();
+ browser.close();
 
  res.set('Content-Type', 'image/png');
  res.send(imageBuffer);