npm script errors when called from gitbash

Gitbash is able to run commands fine when typed directly into the prompt, but when called from npm scripts it outputs errors.

```bash
$npm run get-challenge 01
```
this calls: `which bash` ./code-challenges/bin/get-challenge.sh
but gitbash ouputs that which is not a command, but works fine when typed into the gitbash prompt directly.