Bump tox from 3.1.2 to 3.2.1

Bumps [tox](https://github.com/tox-dev/tox) from 3.1.2 to 3.2.1.
- [Release notes](https://github.com/tox-dev/tox/releases)
- [Changelog](https://github.com/tox-dev/tox/blob/master/CHANGELOG.rst)
- [Commits](tox-dev/tox@3.1.2...3.2.1)

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

Author: dependabot-support

dev-requirements.txt

@@ -6,7 +6,7 @@ Flask==1.0.2
 
 # Testing
 pytest==3.7.1
-tox==3.1.2
+tox==3.2.1
 faker==0.8.17
 
 # Syntax checking