add `-m` flag to git commit for section I5.

without the `-m` flag an error will be displayed. This is the same error that was in [my previous pull request](https://github.com/JumpstartLab/curriculum/pull/644) but in a different section of the tutorial.
Merge pull request #646 from oblakeerickson/patch-5

add `-m` flag to git commit for section I5.