Merge pull request kiawin#29 from kiawin/dependabot/pip/tox-3.14.1

Bump tox from 2.3.1 to 3.14.1

Author: kiawin

requirements_dev.txt

@@ -3,7 +3,7 @@ bumpversion==0.5.3
 wheel==0.29.0
 watchdog==0.8.3
 flake8==2.6.2
-tox==2.3.1
+tox==3.14.1
 coverage==4.1
 Sphinx>=1.4,<1.5
 cryptography==2.3.1