Links to .NET Foundation web site use HTTP instead of HTTPS

[Eilon]

It appears that HTTPS works just fine: https://www.dotnetfoundation.org/

But the links at these places use HTTP:

1. The link in the header of https://github.com/dotnet/home
2. The link in the header of https://github.com/dotnet
3. Some links in https://github.com/dotnet/home/blob/master/README.md (both to .NET Foundation, and a GitHub link to another project)

These links should all change to HTTPS.