Update tox from 2.8.1 to 2.8.2

Author: pyup-bot

requirements_dev.txt

@@ -30,7 +30,7 @@ snowballstemmer==1.2.1
 Sphinx==1.6.3
 sphinx-rtd-theme==0.2.4
 sphinxcontrib-websupport==1.0.1
-tox==2.8.1
+tox==2.8.2
 urllib3==1.22
 virtualenv==15.1.0
 watchdog==0.8.3          # required by watchmedo