adveres

Update PyYAML to >= 5.4 for CVE-2020-14343

1

Hello! I'm encountering a security failure for `pipenv check` using one of these base images. ## Issue * IMAGE: `tiangolo/uvicorn-gunicorn:python3.8-slim-2020-12-19` * [CVE-2020-14343](https://nvd.nist.gov/vuln/detail/CVE-2020-14343) ``` #9 11.44 Checking PEP 508 requirements... #9...