checkIndexBounds off by 1 validation

checkIndexBounds is too lenient and allows setting indexes from 0 .. count inclusive, whereas really the only valid values are 0 .. (count-1).

[x] I have searched the issues of this repository and believe that this is not a duplicate.

Current Behavior

The warning is only produced after setting index to children.length + 1:

Here is an example warning I see when I set index = 4 having only 3 children:

Warning: react-swipeable-view: the new index: 4 is out of bounds: [0-3].

Setting index to exactly children.length should already produce a warning. The warning message should also show the correct range of values.

E.g. setting index to 3 should produce this warning when there are only 3 children:

Warning: react-swipeable-view: the new index: 3 is out of bounds: [0-2].

This should produce a warning, but it doesn't:

<SwipeableViews index={3}>
  <div>A</div>
  <div>B</div>
  <div>C</div>
</SwipeableViews>

This is a minor dev nuisance, where the lenience of react-swipable-views is potentially allowing a dev to not detect code defects.