scrollspy: correct event naming of `scroll` and `load' event

event name `scroll.bs.scroll-spy.data-api` is bad in two points.
First:  namespace `bs.scroll-spy` is different to `bs.scrollspy`. Firstone is only used for this event, so I bet it is wrong.
Second: the event `scroll` has nothing to do with the data-api, so I remove it.

The better event name is: `scroll.bs.scrollspy`

And the registration of the `load` event handler should have a namespace. So I change it to `load.bs.scrollspy.data-api`.