to generate .d.ts

```
{
  "compilerOptions": {
    "outDir": "dist",
    "target": "ES2017",
    "declaration": true // it seems this needs to be added in order to generate .d.ts
  },
  "include": ["src"]
}
```
https://www.typescriptlang.org/docs/handbook/declaration-files/dts-from-js.html