graphics/openimageio: update 1.7.17 -> 1.8.17
PR: 224382
Submitted by: Shane Ambler <FreeBSD@ShaneWare.Biz> (maintainer)
Reviewed by: yuri
Relnotes: http://lists.openimageio.org/pipermail/oiio-announce-openimageio.org/2018-December/000039.html
https://github.com/OpenImageIO/oiio/releases