By Bonnie Stiernberg It’s always encouraging when our aging classic rock heroes go out of their way to keep up with the times and sing the praises of contemporary artists, whether it’s Paul McCartney shouting out St. Vincent and Khruangbin or even Mick Jagger (rather dubiously) declaring Machine Gun Kelly to be the future of rock ‘n’ roll. Regardless of whether or not you agree with their taste in modern music, at the very least it signals a refreshing willingness to stay engaged with pop culture rather than falling into stereotypical “everything was better when I was young” curmudgeonry. In o…