extra space in long bar charts

[ph98]

Thanks for using nivo

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Describe/explain the bug
A clear and concise description of what the bug is.

To Reproduce
Please include a test case that demonstrates the issue you're reporting on a platform like codesandbox, I already have several existing examples on codesandbox, you can fork one of them
depending on the component you're working on: https://codesandbox.io/u/plouc/sandboxes.
This is very critical to maintainers in order to help us see the issue you're seeing.

https://codesandbox.io/s/wispy-glitter-r392l6?file=/src/App.js

Steps to reproduce the behavior:

1. apply an large array to the data source of the chart.

Expected behavior
A clear and concise description of what you expected to happen.

I expect the margin to be close to zero, but now it will be so high when we apply a large array.

Screenshots
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Desktop (please complete the following information):

• OS: [e.g. iOS]
• Browser [e.g. chrome, safari]
• Version [e.g. 22]

Smartphone (please complete the following information):

• Device: [e.g. iPhone6]
• OS: [e.g. iOS8.1]
• Browser [e.g. stock browser, safari]
• Version [e.g. 22]

Additional context
Add any other context about the problem here.

[plouc]

Hi @ph98,

This is due to rounding on the index scale (which becomes quite noticeable with large charts), you can fix this by disabling it:

indexScale={{
    type: 'band',
    round: false,
}}