DETROIT — Birdies are plentiful at the Rocket Mortgage Classic, which is why Tony Finau was kicking himself — just a little bit — even after carding an 8-under 64 to take the first-round lead Thursday at Detroit Golf Club. What could Finau be upset about, especially considering he was just days removed from a win at the 3M Open, the third title of his PGA Tour career? Probably the fact the single-round tournament record was there to be matched as Finau lined up a 20-foot birdie putt on the ninth green, his final hole of the day. His putt had the line but it came up just inches short, denying F…