update bootstrap to v4.2.1
update bootstrap to v4.2.1

* `npm update bootstrap`

thomaspark/bootswatch,thomaspark/bootswatch,douglaskastle/bootswatch,nkraft/bootswatch,douglaskastle/bootswatch,nkraft/bootswatch,nkraft/bootswatch,douglaskastle/bootswatch,douglaskastle/bootswatch,thomaspark/bootswatch