[InterNetNews/inn] 3b7a63: Fix version formatting for current snapshot

[Russ Allbery]

  Branch: refs/heads/main
  Home:   https://github.com/InterNetNews/inn
  Commit: 3b7a636548eef2d44335f1782229a0a0084c38b2
      https://github.com/InterNetNews/inn/commit/3b7a636548eef2d44335f1782229a0a0084c38b2
  Author: Russ Allbery <eagle at eyrie.org>
  Date:   2021-09-13 (Mon, 13 Sep 2021)

  Changed paths:
    M support/mksnapshot

  Log Message:
  -----------
  Fix version formatting for current snapshot

Fix multiple problems with how the date-based version for the
Git snapshot from main was generated.