Add additional challenge for git conflicts

We talk about git helping resolve conflicts when two or more people make changes, but don't really ask students to think about the issue of more than two people making changes. So I added a challenge that would ask the student to try a three-way conflict.
Could you revert the changes in lines 310-312 (since only join the lines) and amend the changes? After you revert it

~~~
$ git add -u
$ git commit --amend
~~~