Fix uid index definition so it also works with MongoDB 3.4 which performs more strict index validation.
Fix uid index definition so it also works with MongoDB 3.4 which
performs more strict index validation.

Plexxi/st2,Plexxi/st2,Plexxi/st2,StackStorm/st2,nzlosh/st2,tonybaloney/st2,StackStorm/st2,StackStorm/st2,tonybaloney/st2,nzlosh/st2,nzlosh/st2,tonybaloney/st2,nzlosh/st2,StackStorm/st2,Plexxi/st2