Bump pyyaml from 3.11 to 5.4

Bumps [pyyaml](https://github.com/yaml/pyyaml) from 3.11 to 5.4.
- [Release notes](https://github.com/yaml/pyyaml/releases)
- [Changelog](https://github.com/yaml/pyyaml/blob/master/CHANGES)
- [Commits](yaml/pyyaml@3.11...5.4)

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

Author: dependabot[bot]

requirements.txt

@@ -1,5 +1,5 @@
 Django==1.7.1
-PyYAML==3.11
+PyYAML==5.4
 cov-core==1.15.0
 coverage==3.7.1
 py==1.4.26