FoliumのHeatMapWithTimeがプロットされなくなった

# 問題
Foliumを使って時系列のヒートマップを地図上に描写しようとしたところ、HeatMapWithTimeの結果が全く反映されなくなっていた。foliumのバージョンは0.10.0。


# 原因
htmlを裏で動かしているLeafletのバージョンが更新され、TimeDimensionに関する部分が変更されたのが原因。
詳しくはfoliumのissue[foliumのissue](https://github.com/python-visualization/folium/issues/1221)を参照。

# 解決策
[https://github.com/python-visualization/folium/pull/1228/files](https://github.com/python-visualization/folium/pull/1228/files)を参考にHeatMapWithTimeのクラスを継承したHeatMapWithTimeFixを作成した。

```python:HeatMapWithFix
from branca.element import CssLink, Element, Figure, JavascriptLink

class HeatMapWithTimeFix(HeatMapWithTime):
    def render(self, **kwargs):
        super(HeatMapWithTime, self).render(**kwargs)
        figure = self.get_root()
        assert isinstance(figure, Figure), ('You cannot render this Element '
                                            'if it is not in a Figure.')

        figure.header.add_child(
            JavascriptLink('https://rawcdn.githack.com/nezasa/iso8601-js-period/master/iso8601.min.js'),  # noqa
            name='iso8601')

        figure.header.add_child(
            JavascriptLink('https://rawcdn.githack.com/socib/Leaflet.TimeDimension/master/dist/leaflet.timedimension.min.js'),  # noqa
            name='leaflet.timedimension.min.js')
        figure.header.add_child(
            JavascriptLink(
                'https://rawcdn.githack.com/python-visualization/folium/master/folium/templates/pa7_hm.min.js'),  # noqa
            name='heatmap.min.js')
        figure.header.add_child(
            JavascriptLink('https://rawcdn.githack.com/pa7/heatmap.js/develop/plugins/leaflet-heatmap/leaflet-heatmap.js'),  # noqa
            name='leaflet-heatmap.js')
        figure.header.add_child(
            CssLink('http://apps.socib.es/Leaflet.TimeDimension/dist/leaflet.timedimension.control.min.css'),  # noqa
            name='leaflet.timedimension.control.min.css')
        figure.header.add_child(
            Element(
                """
            <script>
                var TDHeatmap = L.TimeDimension.Layer.extend({
            initialize: function(data, options) {
                var heatmapCfg = {
                    radius: 15,
                    maxOpacity: 1.,
                    scaleRadius: false,
                    useLocalExtrema: false,
                    latField: 'lat',
                    lngField: 'lng',
                    valueField: 'count',
                    defaultWeight : 1,
                };
                heatmapCfg = $.extend({}, heatmapCfg, options.heatmapOptions || {});
                var layer = new HeatmapOverlay(heatmapCfg);
                L.TimeDimension.Layer.prototype.initialize.call(this, layer, options);
                this._currentLoadedTime = 0;
                this._currentTimeData = {
                    data: []
                    };
                this.data= data;
                this.defaultWeight = heatmapCfg.defaultWeight || 1;
            },
            onAdd: function(map) {
                L.TimeDimension.Layer.prototype.onAdd.call(this, map);
                map.addLayer(this._baseLayer);
                if (this._timeDimension) {
                    this._getDataForTime(this._timeDimension.getCurrentTime());
                }
            },
            _onNewTimeLoading: function(ev) {
                this._getDataForTime(ev.time);
                return;
            },
            isReady: function(time) {
                return (this._currentLoadedTime == time);
            },
            _update: function() {
                this._baseLayer.setData(this._currentTimeData);
                return true;
            },
            _getDataForTime: function(time) {
                    delete this._currentTimeData.data;
                    this._currentTimeData.data = [];
                    var data = this.data[time-1];
                    for (var i = 0; i < data.length; i++) {
                        this._currentTimeData.data.push({
                                lat: data[i][0],
                                lng: data[i][1],
                                count: data[i].length>2 ? data[i][2] : this.defaultWeight
                            });
                        }
                    this._currentLoadedTime = time;
                    if (this._timeDimension && time == this._timeDimension.getCurrentTime() && !this._timeDimension.isLoading()) {
                        this._update();
                    }
                    this.fire('timeload', {
                        time: time
                    });
                }
        });
        L.Control.TimeDimensionCustom = L.Control.TimeDimension.extend({
            initialize: function(index, options) {
                var playerOptions = {
                    buffer: 1,
                    minBufferReady: -1
                    };
                options.playerOptions = $.extend({}, playerOptions, options.playerOptions || {});
                L.Control.TimeDimension.prototype.initialize.call(this, options);
                this.index = index;
                },
            _getDisplayDateFormat: function(date){
                return this.index[date.getTime()-1];
                }
            });
            </script>
                """,  # noqa
                template_name='timeControlScript'
            )
        )
```