Jest coverage for all folders

Hi,
Instead of using
```
"collectCoverageFrom": [
"src/*.{js,ts}"
]
```
Which only coverage the files under `src`, **not including** files in subfolders.

I suggest that change it into:
```
"collectCoverageFrom": [
"src/**/*.{js,ts}"
]
```

I took sometime to figure this out since I'm new to Jest.
Hope this will help others like me.

I've created a PR if you agreed with me 😃