If the values are close, the chart won't animate

* [x] I've read, understood, and done my best to follow the [*CONTRIBUTING guidelines](https://github.com/jjatie/Charts/blob/master/CONTRIBUTING.md).

## What did you do?
I have a BarChartView with two data entries with the values (1, 1000000) and (2, 1000100). I try to animated the chart.

## What did you expect to happen?
The chart doesn't get animated.

## What happened instead?
If the command is like barChartView.animate(xAxisDuration: 2, yAxisDuration: 2), there will be an empty chart for 2 seconds, that suddenly appears with no animations.
If the values were more far apart (for example, 1000000 and 10), the animation would've worked.

## Charts Environment

**Charts version/Branch/Commit Number:**
**Xcode version:** 9
**Swift version:** 4
**Platform(s) running Charts:** iOS
**macOS version running Xcode:** High Sierra

## Demo Project
https://gist.github.com/rptoma/37cef9c394161dcd074e59a678a0e79c