Bump pyyaml from 5.1.2 to 5.4 (getredash#5442)

Bumps [pyyaml](https://github.com/yaml/pyyaml) from 5.1.2 to 5.4.
- [Release notes](https://github.com/yaml/pyyaml/releases)
- [Changelog](https://github.com/yaml/pyyaml/blob/master/CHANGES)
- [Commits](yaml/pyyaml@5.1.2...5.4)

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

requirements.txt

@@ -20,7 +20,7 @@ blinker==1.4
 psycopg2==2.8.3
 python-dateutil==2.8.0
 pytz>=2019.3
-PyYAML==5.1.2
+PyYAML==5.4
 redis==3.5.0
 requests==2.21.0
 SQLAlchemy==1.3.10