Upgrade all test packages to the latest version

Author: Photonios

requirements/test.txt

@@ -1,10 +1,10 @@
 -r base.txt
 
-psycopg2==2.7.3.2
-coverage==4.4.2
-dj-database-url==0.4.2
-pytest==3.3.2
-pytest-benchmark==3.1.1
-pytest-django==3.1.2
-pytest-cov==2.5.1
-tox==2.9.1
+psycopg2==2.8.2
+coverage==4.5.3
+dj-database-url==0.5.0
+pytest==4.5.0
+pytest-benchmark==3.2.2
+pytest-django==3.4.8
+pytest-cov==2.7.1
+tox==3.11.1