Fix pre-commit hook

scripts/pre-commit.sh

@@ -7,7 +7,7 @@ cd "$(git rev-parse --show-toplevel)"
 
 if git diff --cached --name-only | grep -q '^exercises/'; then
     git stash -q --keep-index
-    rm -f exercises/*.ipynb
+    git rm -f exercises/*.ipynb
     for nb in exercises/solutions/*.ipynb; do
         target="exercises/$(basename "$nb")"
         cat "$nb" | $(git config filter.ipynb-codecells.clean) > "$target"