v3.8.0

Thanks for all the help with PRs etc. Sorry this one took so long to get out. I have some news to share soon. 

## What's Changed
* Add @babel/plugin-transform-nullish-coalescing-operator and @rollup/p… by @loycoder in https://github.com/sampotts/plyr/pull/2783
* Fix #2799 -- drop recommendation of polyfill.io by @amureki in https://github.com/sampotts/plyr/pull/2800
* add Mux as an example in the demo by @dylanjha in https://github.com/sampotts/plyr/pull/2859
* Fixed captions when storage has been disabled by @o0sh4d0w0o in https://github.com/sampotts/plyr/pull/2813
* CORS support for preview thumbnails by @mdkieran in https://github.com/sampotts/plyr/pull/2777
* fix:progress offset by @Wshengs in https://github.com/sampotts/plyr/pull/2750
* docs: fix Koel's tagline and URL by @phanan in https://github.com/sampotts/plyr/pull/2857
* Set PIP support based on the Picture in Picture API by @ryanbrunner in https://github.com/sampotts/plyr/pull/2849
* docs: update the default value of iconUrl by @HADB in https://github.com/sampotts/plyr/pull/2734

## New Contributors
* @loycoder made their first contribution in https://github.com/sampotts/plyr/pull/2783
* @amureki made their first contribution in https://github.com/sampotts/plyr/pull/2800
* @dylanjha made their first contribution in https://github.com/sampotts/plyr/pull/2859
* @o0sh4d0w0o made their first contribution in https://github.com/sampotts/plyr/pull/2813
* @mdkieran made their first contribution in https://github.com/sampotts/plyr/pull/2777
* @Wshengs made their first contribution in https://github.com/sampotts/plyr/pull/2750
* @phanan made their first contribution in https://github.com/sampotts/plyr/pull/2857
* @ryanbrunner made their first contribution in https://github.com/sampotts/plyr/pull/2849
* @HADB made their first contribution in https://github.com/sampotts/plyr/pull/2734

**Full Changelog**: https://github.com/sampotts/plyr/compare/v3.7.8...v3.8.0