Update pytest packages

New version of pytest and friends fix the problems that we have

Author: stsewd

requirements/testing.txt

@@ -2,14 +2,9 @@
 -r local-docs-build.txt
 
 django-dynamic-fixture==2.0.0
-# pytest 4.2 is incompatible with pytest-django 3.4.6
-pytest==4.1.1  # pyup: <4.2
-# pytest-django 3.4.7 break our tests from corporate site
-# probably a bug related to overriding django settings in
-# previous tests
-pytest-django==3.4.6  # pyup: <3.4.7
-# pytest-xdist >1.27 requires pytest >4.1
-pytest-xdist==1.27.0  # pyup: ignore
+pytest==4.6.2
+pytest-django==3.5.0
+pytest-xdist==1.28.0
 pytest-cov==2.7.1
 apipkg==1.5
 execnet==1.6.0