According to the old saying, one shouldn’t fix what hasn’t been broken and that appears to be Vikings coach Mike Zimmer’s take on handling quarterback Case Keenum. Zimmer has resisted naming Keenum the starting quarterback for more than a week at a time all year and isn’t changing that approach in the wake of Keenum’s terrific performance against the Lions on Thanksgiving. Keenum threw two touchdowns and ran for another to continue both his run of great play and the Vikings’ winning streak, but Zimmer said Monday that the starting job will still be decided on a weekly basis.