Refactor dateToRfc822 to use local timezone

[fliptopbox]

Refactor dateToRfc822 to use local timezone:

• Simplify the RFC822 method to use Intl.DateTimeFormat() API, which eliminates the need for hard coded Month and Day arrays, since the API has those features built into its formatting options.
• Also the previous version hard codes the timezone (as +0000), which is awkward for European implementations, where using the timeZoneName is preferable, and more accurate.
• And finally update the unit test to assert the RFC822 string format as proposed, instead of checking the return value of the function against a known artifact.

I created a RFC822 RegEx101 tool for checking the pub date format:
https://regex101.com/library/KGSAUY

[zachleat]

Thank you!