Scheduled monthly dependency update for May (#41)

* Update sphinx from 1.8.3 to 2.0.1

* Update coverage from 4.5.2 to 4.5.3

* Update flake8 from 3.7.4 to 3.7.7

* Update isort from 4.3.4 to 4.3.17

* Update pyflakes from 2.1.0 to 2.1.1

* Update pytest from 4.2.0 to 4.4.1

* Update pytest-isort from 0.2.1 to 0.3.1

* Update pytest-mock from 1.10.0 to 1.10.4

Author: pyup-bot

docs/requirements.txt

@@ -1,4 +1,4 @@
 ansi2html  # pyup: ignore
 Pygments==2.3.1
-Sphinx==1.8.3
+Sphinx==2.0.1
 sphinxcontrib-websupport==1.1.0

tests/requirements.txt

@@ -1,14 +1,14 @@
-coverage==4.5.2
+coverage==4.5.3
 docutils==0.14
-flake8==3.7.4
-isort==4.3.4
+flake8==3.7.7
+isort==4.3.17
 pycodestyle==2.5.0
-pyflakes==2.1.0
+pyflakes==2.1.1
 Pygments==2.3.1
-pytest==4.2.0
+pytest==4.4.1
 pytest-cov==2.6.1
-pytest-isort==0.2.1
-pytest-mock==1.10.0
+pytest-isort==0.3.1
+pytest-mock==1.10.4
 pytest-sugar==0.9.2
 pytest-toolbox==0.4
 numpy  # pyup: ignore