Update CalendarHeatmap documentation

[oscarlofwenhamn]

I'm submitting a...

[ ] Regression (a behavior that used to work and stopped working in a new release)
[ ] Bug report  
[ ] Performance issue
[ ] Feature request
[x] Documentation issue or request
[ ] Other... Please describe:

Current behavior

Using the current code and sample data from the CalendarHeatmap code at Reaviz Charts page gives the Error Uncaught TypeError: date.getFullYear is not a function. When instead passing the keys as Date objects, it renders. The docs and sample data should be updated to reflect this.

[oscarlofwenhamn]

I could find the cached version of the same issue from the last repo with the following reply:

Hi @elimist3. This component actually requires Date instances to be passed as keys in the data. I forked your codesandbox here and converted the keys to date and it works:

https://codesandbox.io/s/reaviz-codesandbox-template-6ew0d

Seems to work in my case as well, but I reckon the docs can still do with an update reflecting this.

[amcdnl]

Can you verify if this works now?

[oscarlofwenhamn]

Verified, sample data now works as-is, nice!