Use poetry in CI

.gitlab-ci.yml

@@ -5,6 +5,6 @@ test:
   variables:
     PYTHONPATH: '.'
   script:
-    - pip install -r requirements.txt
-    - pip install -r dev_requirements.txt
-    - pytest -v
+    - curl -sSL https://raw.githubusercontent.com/python-poetry/poetry/master/get-poetry.py | python
+    - poetry install
+    - poetry run pytest tests -v