ContributionChartValue should have `count` property or dynamic via accessor

[abhidatta0]

There is a weak TS support when writing logic on the tooltipDataAttrs value param. Currently this is the structure:

type ContributionChartValue = {
    value: number;
    title: string;
    tooltipDataAttrs: TooltipDataAttrs;
    date: Date;
};

This is different from what we actually find by logging the value (as per the values data in the example)

{"value": {"count": 4, "date": "2017-04-02"}}
{"value": {"count": null, "date": null}}