Update course-challenge.md

[trogfield]

added v2

[elmoallistair]

Thanks for your contribution but please note this:

1. Don't spam pull requests, create one big pull request instead just one pull per commit
2. Continue the question number, no need to add another version, there are multiple questions added per question number, but user only get one of them.
3. Don't use new question format, follow the previous format for consistency:

### Question number
question description

* answer_option1
* answer_option2
* answer_option3
* answer_option4 (bold the correct answer)

> correct answer description