setting <5 in reqs_dev for pytest - pytest 6 seems to cause probs with --basetemp

requirements_dev.txt

 # contains all requirements to run the tests by running ```tox -e py36,py37```
 tox>=3.5.2
-pytest>=3.8.2
+pytest>=3.8.2,<5
 pytest-runner>=4.2
 Click>=7.0
 crowdai-api>=0.1.21