disable extensions and google translate by default (#774)

This patch teaches `puppeteer.launch` to run chromium with disabled
chrome extensions and google translate services.

References #760

lib/Launcher.js

@@ -32,10 +32,12 @@ const DEFAULT_ARGS = [
   '--disable-background-timer-throttling',
   '--disable-client-side-phishing-detection',
   '--disable-default-apps',
+  '--disable-extensions',
   '--disable-hang-monitor',
   '--disable-popup-blocking',
   '--disable-prompt-on-repost',
   '--disable-sync',
+  '--disable-translate',
   '--enable-automation',
   '--enable-devtools-experiments',
   '--metrics-recording-only',