Changing name of vite config from .ts (typescript) to .mjs (javascrip…

…t module) avoids vite deprecation message.

Vite deprecation message looks like:

```
remote:        Build with Vite complete: /tmp/build_93418466/public/vite
remote:        The CJS build of Vite's Node API is deprecated. See https://vitejs.dev/guide/troubleshooting.html#vite-cjs-node-api-deprecated for more details.
```

And started in vite 5.x.

Relation to .ts typescript and simple solution suggested from ElMassimo/vite_ruby#431

Seems to work great.