Bump pyyaml from 5.1.2 to 5.3.1

Bumps [pyyaml](https://github.com/yaml/pyyaml) from 5.1.2 to 5.3.1.
- [Release notes](https://github.com/yaml/pyyaml/releases)
- [Changelog](https://github.com/yaml/pyyaml/blob/master/CHANGES)
- [Commits](yaml/pyyaml@5.1.2...5.3.1)

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

Author: dependabot-preview[bot]

requirements.txt

@@ -4,7 +4,7 @@ pymatgen==2020.01.28
 xgboost==0.80
 tpot==0.11.0
 skrebate==0.6
-pyyaml==5.1.2
+pyyaml==5.3.1
 scikit-learn==0.22.2
 
 # Also requirements of matminer