Exclude mlflow/protos (#5036)

Signed-off-by: harupy <17039389+harupy@users.noreply.github.com>

hooks/pre-commit

@@ -3,6 +3,12 @@ set -ex
 diff=$(git diff --cached --name-only | grep '\.py$' || true)
 
 if [ ! -z "$diff" ]; then
-  black --check $diff
+  # We specify `--exclude` option in `pyproject.toml`,
+  # but it's only consulted for recursive search, not for files passed on the command line:
+  # https://github.com/psf/black/issues/438#issuecomment-413886281
+  # `--force-exclude` option can solve this issue, but black >= 20.8b0 is required:
+  # https://black.readthedocs.io/en/stable/change_log.html#id26
+  # TODO: Upgrade black to >= 20.8b0 and use `--force-exclude`
+  black --check $(echo $diff | grep -v '^mlflow/protos')
   pylint $diff
 fi