Add an animated icon to the map example

[ddrempe]

Hello,

I've implemented some minimal working example of Add an animated icon to the map with react-map-gl.

Here is the codesandbox: https://codesandbox.io/s/react-map-gl-animated-icon-ktors0

Even though it is working, I find it hacky and would like to rewrite it in more Reactish way and if possible:

• avoid referencing with this inside of the `pulsingDot
• avoid declaring helper canvas element

Any ideas/suggestions?