pytest: use latest version

(cherry picked from commit 55717c4751b970de86a09e26277b4fdce37effb2)

requirements.d/development.txt

@@ -3,7 +3,7 @@ setuptools_scm
 pip
 virtualenv
 tox
-pytest!=3.3.0
+pytest
 pytest-xdist
 pytest-cov
 pytest-benchmark