In short, in the deadly_skills branch, try getting rid of the question mark in the last line of introduction.md (* Killing history using git rebase
?), so you have
* Killing history using git rebase
Then merge deadly_skills back into master, and tag that commit.
Looking at your repo., the issue could be that the original merge (a71296b6b3530c59e284b732db109bce2b8097df) request from deadly_skills to master didn't have the line required from the last challenge of 2.7
Killing history using git rebase
So, I think that would've been the merge to tag, but maybe CS is looking in the introduction.md file and looking for that line, which doesn't exist in that particular commit.
And, in your more recent merge commit, you have a question mark at the end. I'd be surprised that's causing the problem, as that's a pretty specific thing to look for, but it's worth a try.
As I say above, make that correction on deadly_skills, merge it into master, and tag that merge commit.
Hopefully the merge with the correct change doesn't have to be done in the context of the CS pull request. It's I think possible to re-do all that, but that may get tricky.