fix docstring in build_classifier.py

[sandylaker]

Short Description

Long Description

Fix docstring in saliency_metrics/models/build_classifier.py.

Checklist

• [x] Code linting are passed. (Please run pre-commit run --all-files).
• [x] Mypy checks are passed. (Please run mypy saliency_metrics).
• [x] Unit tests are added for new code.
• [x] Documentation is added for the new code.
• [x] Unit tests are passed. (Please run sh tests/run_tests.sh).
• [x] Docs are successfully built. (Please run cd docs/ && make html and host the webpage locally).