Purple Static Map Regions

[reustle]

It seems that the static map is rendering No cases areas as purple for some reason. We should set that to some color with opacity 0.

This seems related:

• https://github.com/reustle/covid19japan/blob/master/src/data/helper.js#L48
• https://github.com/reustle/covid19japan/blob/master/src/data/constants.js#L32