`bottomOffset` prop does not seem to work?

Hi! First off, great job making this library! This thing solves a common problem in a real nice way and really appreciate the time taken to create it!

Been trying to use it in my project and I can see the `onEnter` and `onLeave` handlers being triggered nicely which is awesome.

The issue I'm facing though is when I send a `bottomOffset` prop value of any kind (positive OR negative pixel/percentage string or number), `Waypoint` does not seem to honor it at all and doesn't adjust the bottomOffset boundary as I expect it to.

In my use case, `Waypoint` is wrapping around a custom component I made in my project. Essentially like this:

```

{...}

```

Any thoughts as to why the `bottomOffset` does not adjust?