In Unity 2019.1.14f1, I couldn't open the vanilla package within Unity without manifest issues:

Deleting the manifest to allow it to auto-regenerate seemed to do the trick. Perhaps rename the manifest file to .bak extension, then .ignore the real one? This would allow users to auto-generate the manifest regardless of their Unity ver and without issues.
A temporary, quick alternative would be to put this in the README.
In Unity 2019.1.14f1, I couldn't open the vanilla package within Unity without manifest issues:
Deleting the manifest to allow it to auto-regenerate seemed to do the trick. Perhaps rename the manifest file to
.bakextension, then.ignorethe real one? This would allow users to auto-generate the manifest regardless of their Unity ver and without issues.A temporary, quick alternative would be to put this in the README.