Update test requirements.

test_requirements.txt

@@ -1,12 +1,12 @@
 appdirs==1.4.3
 atomicwrites==1.3.0
-attrs==19.1.0
+attrs==19.3.0
 black==19.3b0; python_version >= '3.6'
 click==7.0
 colorama==0.4.1
 coverage==4.5.4
 docopt==0.6.2
-flake8==3.7.8
+flake8==3.7.9
 flexmock==0.10.4
 isort==4.3.21
 mccabe==0.6.1
@@ -16,8 +16,8 @@ py==1.8.0
 pycodestyle==2.5.0
 pyflakes==2.1.1
 pykwalify==1.7.0
-pytest==5.1.2
-pytest-cov==2.7.1
+pytest==5.2.2
+pytest-cov==2.8.1
 python-dateutil==2.8.0
 PyYAML==5.1.2
 requests==2.22.0