Remove python3.5 compatibility

.gitlab-ci.yml

 stages:
-  - py35
   - py36
   - py37
   - py38
   - py39
-test-py3.5:
-  image: python:3.5
-  stage: py35
-  script:
-  - pip3 install -r requirements.txt
-  - python3.5 -m pytest --cov rpg tests
 test-py3.6:
   image: python:3.6
   stage: py36