Bump pyyaml from 3.13 to 5.4 in /opendata

Bumps [pyyaml](https://github.com/yaml/pyyaml) from 3.13 to 5.4.
- [Release notes](https://github.com/yaml/pyyaml/releases)
- [Changelog](https://github.com/yaml/pyyaml/blob/master/CHANGES)
- [Commits](yaml/pyyaml@3.13...5.4)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

opendata/requirements.txt

@@ -1,7 +1,7 @@
 pandas==0.23.4
 numpy==1.15.3
 yamlordereddictloader==0.4.0
-PyYAML==3.13
+PyYAML==5.4
 ddlparse==1.1.1
 jours-feries-france==0.5.1
 vacances-scolaires-france==0.8.0