It's another rumor from a retailer, but this one has more credibility than most, because it's more than just a listing for GTA V on the PC, Xbox One, or PS4 found on a retailer's website. The German retailer Saturn.de Tweeted:
Translated, that means:
Because I was just asked: the release of #GTAV for PC and XBOX one PS4 is expected for June. #rumors #abgeNICKt
Of course, many false rumors have come out before, so don't set too much stock in this. Maybe all the rumors alone will convince Rockstar to make an official announcement.