simplepie: Update to the latest simplepie from github

[talgalili]

Simplepie started merging pull requests as of today (mostly bug fixes), thanks to a new maintainer receiving access to the repo from the original founder of the library.

Please include the latest working branch in the next WP version:
​https://github.com/simplepie/simplepie

Thanks,
Tal

[talgalili]

(since most updates are bug fixes - I am changing this from enhancement to bug)

[rmccue]

Right now, there's no new releases, but rest assured I'm staying on top of the latest updates. :)