Update to new Chrome headless mode

Updates to us Puppeteer with the new Chrome headless mode.

• https://developer.chrome.com/articles/new-headless/
• https://github.com/puppeteer/puppeteer#default-runtime-settings

Seems to be ~10% faster to generate a PDF and ensures the output is the same as the Chrome browser output.

Also updated to pagedjs@0.4.2