YAxis tickCount not working as expected

Hi, I found that when I change YAxis `tickCount` prop it works improperly. Here is a line chart with a brush.

Here `tickCount` is not set for both chart and brush

Here `tickCount` is set to 5 for both charts

Here `tickCount` is set to 2 for both charts

As you can see it works weirdly for both charts. For the bottom one, it distributes ticks unevenly. I expected the only two ticks to be at the top and the bottom most parts of the scale. For the top one, it just doesn't make any sence.

I am using the latest version `0.12.8`
Here is the component's [source code](https://pastebin.com/Js5zhzVj)