Constrain multi-slider values to within min/max range.

[pepopowitz]

Addresses the “range out of scope” issue - https://github.com/davidchin/react-input-range/issues/117

The issue was happening on a multi-value slider with a wide range of accepted values, when you click on the "outside" edge of the handle.

For example, if the range slider goes from 1 to 100, and my min is on 1, I could make the min go to -1 by clicking on the left edge of the handle and letting go.

I added two tests - one for the min, one for the max.