sshuttle: 0.74 -> 0.76

And back to fetchurl we go:

  “LookupError: setuptools-scm was unable to detect version for
   '/tmp/nix-build-.../sshuttle-v0.76-src'. Make sure you're not
   using GitHub's tarballs (or similar ones), as those don't
   contain the necessary metadata. Use PyPI's tarballs instead.”