Update Cloudflare CDN url in readme

[austencm]

Checklist

• Is this an issue with code?: [No]
• Is this an issue with documentation?: [Yes]
• Have you checked for similar open issues?: [Yes]

Please remember that this is an issue tracker, support requests should be posted on StackOverflow - see CONTRIBUTING.md

Please describe your issue in as much detail as possible:

The Cloudflare url in the readme is for version 2.0.3. I found out the hard way that this isn't the newest version because the stagger option does not work in 2.0.3. Hopefully updating this will save someone else a headache.