dev-python/aiodns: use correct typing distribution

dev-python/aiodns: use correct typing distribution

With the Gentoo startfiles for Python the typing distribution for
Python 3.6  and Python 3.7 is searched as external library and not as
part of the standard library.

Backport fix from https://github.com/saghul/aiodns/commit/281112107c742a3e24e8bce2cb09c3c4d9d01b6d

Closes: https://github.com/gentoo/gentoo/pull/13324
Closes: https://bugs.gentoo.org/692720
Package-Manager: Portage-2.3.69, Repoman-2.3.16
Signed-off-by: Gerion Entrup <gerion.entrup@flump.de>
Signed-off-by: Zac Medico <zmedico@gentoo.org>