Revert smoke test accidentally default to non headless mode.

test/smoke_test.js

@@ -15,7 +15,7 @@ const path = require('path');
 (async () => {
   const browser = await puppeteer.launch({
     // when debugging localy setting headless to "false" can be very helpful
-    headless: false,
+    headless: true,
     args: ["--disable-local-storage", "--no-sandbox"]
   });
   const page = await browser.newPage();