Fix up for 2c1cd46167
We keep the `.mjs` fragment within the filename to avoid changing it manually within the renamed `purify.es.js` file. Given the `.map` extension, it will not affect the nginx (or others) mimetypes configuration.
It requires a special nginx configuration that we want to avoid for all instances deployments:
```
include mime.types;
types {
application/javascript mjs;
}
```
simple-statistics has a few advantages:
- faster
- more accurate kmeans algo
- Jenks-Fisher algo
Also, I suspect will use it again for next step, which is Bubble
mode layer.
