Bump py from 1.5.2 to 1.8.0

Bumps [py](https://github.com/pytest-dev/py) from 1.5.2 to 1.8.0.
- [Release notes](https://github.com/pytest-dev/py/releases)
- [Changelog](https://github.com/pytest-dev/py/blob/master/CHANGELOG)
- [Commits](pytest-dev/py@1.5.2...1.8.0)

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

requirements.txt

@@ -16,7 +16,7 @@ MarkupSafe==1.0
 mccabe==0.6.1
 pluggy==0.6.0
 psycopg2==2.7.3.2
-py==1.5.2
+py==1.8.0
 pycodestyle==2.3.1
 pyflakes==1.6.0
 pytest==3.4.0