sys-apps/portage: version bump to 2.3.64

sys-apps/portage: version bump to 2.3.64

Bug 378603 - New (council approved) default locations for the Gentoo
repository, distfiles, and binary packages (does not apply to installed
systems using the old defaults):

  /usr/portage -> /var/db/repos/gentoo
  /usr/portage/distfiles -> /var/cache/distfiles
  /usr/portage/packages -> /var/cache/binpkgs

Bug: https://bugs.gentoo.org/378603
Bug: https://bugs.gentoo.org/683434
Package-Manager: Portage-2.3.64, Repoman-2.3.12
Signed-off-by: Zac Medico <zmedico@gentoo.org>