dist: Update VERSION to 3.1.3a1#5579

jsquyres merged 1 commit intoopen-mpi:v3.1.xopen-mpi/ompi:v3.1.xfrom

bwbarrett:v3.1.x-VERSIONbwbarrett/ompi:v3.1.x-VERSIONCopy head branch name to clipboard