Calendar crashes when no data is present

[mdorr]

If no data is present (yet), the calendar component crashes with the following error:

Uncaught TypeError: Cannot read property 'value' of undefined
    at nivo-calendar.js:510
    at new WithPropsOnChange (withPropsOnChange.js:52)
   [...][1]

This causes an issue if p.e. the component is still waiting for data to be loaded asynchronously. The error is caused by in /packages/nivo-calendar/src/enhance.js:

if (domain === 'auto') {
  colorDomain = [minBy(data, 'value').value, maxBy(data, 'value').value]
}

If no data is given, minBy/maxBy will return undefined, and then .value is called on that. To prevent this from happening, _.get can be used, which will safely return undefined instead of throwing an error. I'll submit a pull request in a moment.

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[1] Error message shortened for clarity. Full trace in attachment: nivo-calendar-error.txt