Bump pytest from 3.2.3 to 3.3.1

Bumps [pytest](https://github.com/pytest-dev/pytest) from 3.2.3 to 3.3.1.
- [Changelog](https://github.com/pytest-dev/pytest/blob/master/CHANGELOG.rst)
- [Commits](https://github.com/pytest-dev/pytest/compare/3.2.3...3.3.1)

requirements.txt

@@ -11,7 +11,7 @@ itsdangerous==0.24
 Jinja2==2.10
 MarkupSafe==1.0
 PyMySQL==0.7.11
-pytest==3.2.3
+pytest==3.3.1
 PyYAML==3.12
 raven==6.3.0
 requests==2.18.4