[heat][heat-translator] add Hiroyuki Jo to heat-translator core reviewer

Hi all Hiroyuki Jo has been active in the past few months. Also, he raises his willingness to help maintain patches in the last PTG [1]. It's my pleasure to add Hiroyuki Jo to heat-translator-core team with condition that me and other core members should help to review his patch (so no self-approval) and provide review guideline if needed. Free feel to suggest otherwise. [1] https://etherpad.openstack.org/p/PVG-heat -- May The Force of OpenStack Be With You, *Rico Lin*irc: ricolin