Bump pyyaml from 5.3.1 to 5.4

Bumps [pyyaml](https://github.com/yaml/pyyaml) from 5.3.1 to 5.4.
- [Release notes](https://github.com/yaml/pyyaml/releases)
- [Changelog](https://github.com/yaml/pyyaml/blob/master/CHANGES)
- [Commits](yaml/pyyaml@5.3.1...5.4)

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

Author: dependabot[bot]

requirements.txt

@@ -4,7 +4,7 @@ tweepy~=3.9.0
 python-dateutil~=2.8.2
 networkx~=2.5
 nltk~=3.5
-PyYAML~=5.3.1
+PyYAML~=5.4
 schedule~=0.6.0
 tqdm~=4.50.0
 numpy~=1.19.2