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.client.txt

@@ -15,7 +15,7 @@ WTForms==2.0.2
 Flask-WTF==0.12
 typing
 click==6.7
-pyyaml==3.13
+pyyaml==5.1
 requests
 future
 -e svn+https://llvm.org/svn/llvm-project/llvm/trunk/utils/lit/#egg=lit