Scheduled monthly dependency update for December (#14)

* Update pip from 18.0 to 18.1

* Update wheel from 0.32.0 to 0.32.3

* Update flake8 from 3.5.0 to 3.6.0

* Update tox from 3.4.0 to 3.5.3

* Update coverage from 4.5.1 to 4.5.2

* Update sphinx from 1.8.1 to 1.8.2

* Update pytest from 3.8.1 to 4.0.1

requirements_dev.txt

@@ -1,14 +1,14 @@
-pip==18.0
+pip==18.1
 bumpversion==0.5.3
-wheel==0.32.0
+wheel==0.32.3
 watchdog==0.9.0
-flake8==3.5.0
-tox==3.4.0
-coverage==4.5.1
+flake8==3.6.0
+tox==3.5.3
+coverage==4.5.2
 six==1.11.0
-Sphinx==1.8.1
+Sphinx==1.8.2
 twine==1.12.1
 
 mock==2.0.0
-pytest==3.8.1
+pytest==4.0.1
 pytest-runner==4.2