Scheduled weekly dependency update for week 07 (#42)

* Update pip from 18.1 to 19.0.2

* Update wheel from 0.32.3 to 0.33.0

* Update flake8 from 3.6.0 to 3.7.5

* Update tox from 3.6.1 to 3.7.0

* Update sphinx from 1.8.3 to 1.8.4

* Update cryptography from 2.4.2 to 2.5

* Update twine from 1.12.1 to 1.13.0

requirements_dev.txt

@@ -1,12 +1,12 @@
-pip==18.1
+pip==19.0.2
 bumpversion==0.5.3
-wheel==0.32.3
+wheel==0.33.0
 watchdog==0.9.0
-flake8==3.6.0
-tox==3.6.1
+flake8==3.7.5
+tox==3.7.0
 coverage==4.5.2
-Sphinx==1.8.3
-cryptography==2.4.2
+Sphinx==1.8.4
+cryptography==2.5
 PyYAML==3.13
-twine==1.12.1
+twine==1.13.0