Build script does (will) not work for some Linux distros(?)

**Describe the bug**
When running `yarn build`, the command `cp -r ./web-app/build/ ./builld` copies the `./web-app/build` to `./build/build` folder.

I think the right command would be:

See https://askubuntu.com/a/86824

```
cp -r ./web-app/build/. ./build/ # notice the dot
```

**Desktop (please complete the following information):**
 - Platform: Linux
 - OS: Fedora
 - Version 31
