update link to whatwg/fs

Author: jimmywarting

README.md

@@ -3,7 +3,7 @@ StreamSaver.js (legacy-ish)
 
 ... Don't worry it's not deprecated. It's still maintained and i still recommend 
 using this when needed. Just want to let you know that there is this new native way
-to save files to the HD: https://wicg.github.io/native-file-system which is more
+to save files to the HD: https://github.com/whatwg/fs which is more
 or less going to make FileSaver, StreamSaver and similar packages a bit obsolete
 in the future, it'still in a experimental stage and not implemented by all browser.
 That is why I also built [native-file-system-adapter](https://github.com/jimmywarting/native-file-system-adapter)