I forgot to bump the configure.ac version before tagging the 2.1.0~beta1
release. Since we cannot remove old tags (see “On Re-tagging” in git-tag(1)),
we have to call this release 2.1.0~beta2.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>
Reviewed-by: Olivier Tharan <olive@google.com>