Bump pyyaml from 3.12 to 5.1

Bumps [pyyaml](https://github.com/yaml/pyyaml) from 3.12 to 5.1.
- [Release notes](https://github.com/yaml/pyyaml/releases)
- [Changelog](https://github.com/yaml/pyyaml/blob/master/CHANGES)
- [Commits](yaml/pyyaml@3.12...5.1)

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

Author: dependabot[bot]

requirements.txt

@@ -3,5 +3,5 @@ greenlet==0.4.13
 Mako==1.0.6
 MarkupSafe==1.0
 pathtools==0.1.2
-PyYAML==3.12
+PyYAML==5.1
 watchdog==0.8.3

setup.py

@@ -51,7 +51,7 @@
         'Mako==1.0.6',
         'MarkupSafe==1.0',
         'greenlet==0.4.13',
-        'PyYAML==3.12',
+        'PyYAML==5.1',
         'argh==0.26.2',
         'argparse==1.2.1',
         'pathtools==0.1.2',