Don't lint scripts/vendor directory

make lint currently gives me over 600 violations because it lints everything in scripts/vendor, which is not code we write or control.

Let's only include actual Python scripts we place in scripts/

Before

$ make lint | wc -l
make: *** [Makefile:58: flake8] Error 1
669

After

$ make lint | wc -l
All done! ✨ 🍰 ✨
78 files would be left unchanged.
9