Bump pyyaml from 3.13 to 5.1

Bumps [pyyaml](https://github.com/yaml/pyyaml) from 3.13 to 5.1.
- [Release notes](https://github.com/yaml/pyyaml/releases)
- [Changelog](https://github.com/yaml/pyyaml/blob/master/CHANGES)
- [Commits](https://github.com/yaml/pyyaml/compare/3.13...5.1)

Signed-off-by: dependabot[bot] <support@github.com>

requirements.txt

@@ -1,4 +1,4 @@
-PyYAML==3.13
+PyYAML==5.1
 ExifRead==2.3.0
 cloudpickle==1.2.2
 pytz==2020.1