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](yaml/pyyaml@3.13...5.1)

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

Author: dependabot[bot]

requirements.txt

@@ -4,7 +4,7 @@ num2words==0.5.10
 numpy==1.16.4
 praat-parselmouth==0.3.3
 PyAudio==0.2.11
-PyYAML==3.13
+PyYAML==5.1
 scipy==1.2.0
 swaglyrics==1.0.0
 torch==1.1.0