United Airlines has made it official. In a memo to employees United CEO Oscar Munoz said international premium economy is coming to the Chicago-based carrier later this year. Munoz did not specify a particular timeline beyond that, but indicated planes would begin to be outfitted with the new cabin product starting in 2018. If United sticks to that timeline, it would be the last of the three major United States-based carriers with international route systems to introduce a dedicated premium economy…