dev-libs/libmodbus in tree is 3.1.2. =dev-libs/libmodbus-3.1.4 was released on 2016-05-28.
commit 4bb4d9d31c2f2171025d05418d258760a3b892a1 Author: Michael Weber <xmw@gentoo.org> Date: Wed Jan 25 16:15:42 2017 +0100 dev-libs/libmodbus: Version bump. Package-Manager: Portage-2.3.3, Repoman-2.3.1 commit cce2a74a7024b5ae06ed812893ca82fb2c9628ea Author: Michael Weber <xmw@gentoo.org> Date: Wed Jan 25 15:48:12 2017 +0100 dev-libs/libmodbus: Drop old. Package-Manager: Portage-2.3.3, Repoman-2.3.1