Bump py from 1.4.32 to 1.8.1

Bumps [py](https://github.com/pytest-dev/py) from 1.4.32 to 1.8.1.
- [Release notes](https://github.com/pytest-dev/py/releases)
- [Changelog](https://github.com/pytest-dev/py/blob/master/CHANGELOG)
- [Commits](pytest-dev/py@1.4.32...1.8.1)

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

requirements.txt

@@ -6,7 +6,7 @@ mccabe==0.5.3
 mock==2.0.0
 pbr==1.10.0
 pluggy==0.4.0
-py==1.4.32
+py==1.8.1
 pycodestyle==2.2.0
 pyflakes==1.3.0
 pytest==3.0.5