code: function harvest() {
    var q = "DELETE FROM tokens WHERE expires_at < now() AT TIME ZONE 'UTC'";
    db.getClient(function(err, client, done) {
      client.query(q, function(err) {
        if(err) {
          console.error(new Date);
          console.error(err.stack);
        }
        done(err);
      });
    });
  }
docs: Deletes expired tokens