build: Bump mimimum required Automake version.
build: Bump mimimum required Automake version.

* configure.ac (min_automake_version): Bump to 1.16.3.
--

The AM_DISTCHECK_DVI_TARGET variable that we now use has been
introduced in Automake 1.16.3.

Signed-off-by: Damien Goutte-Gattat <3a260918a4ae0abc8ac3e544c6df1814a2596a5f@incenp.org>

gpg/scute,gpg/scute,gpg/scute