Scheduled monthly dependency update for February (#38)

* Update flake8 from 3.6.0 to 3.7.4

* Update pycodestyle from 2.4.0 to 2.5.0

* Update pyflakes from 2.0.0 to 2.1.0

* Update pytest from 4.0.2 to 4.2.0

* Update pytest-cov from 2.6.0 to 2.6.1

Author: pyup-bot

tests/requirements.txt

@@ -1,12 +1,12 @@
 coverage==4.5.2
 docutils==0.14
-flake8==3.6.0
+flake8==3.7.4
 isort==4.3.4
-pycodestyle==2.4.0
-pyflakes==2.0.0
+pycodestyle==2.5.0
+pyflakes==2.1.0
 Pygments==2.3.1
-pytest==4.0.2
-pytest-cov==2.6.0
+pytest==4.2.0
+pytest-cov==2.6.1
 pytest-isort==0.2.1
 pytest-mock==1.10.0
 pytest-sugar==0.9.2