requirements: Make requirements less strict (again)

Still can't build this in copr :(

Signed-off-by: Stephen Finucane <[email protected]>

Author: stephenfin

test-requirements.txt

@@ -1,4 +1,4 @@
 mock~=3.0.0
-pytest>=4.0,<6.0;python_version>='3.5'
-pytest>=4.0,<5.0;python_version=='2.7'
-pytest-cov>=2.7,<3.0
+pytest>=3.0,<6.0;python_version>='3.5'
+pytest>=3.0,<5.0;python_version=='2.7'
+pytest-cov~=2.5