Update .gitlab-ci.yml

.gitlab-ci.yml

+#Specify python version here e.g. python:3.6
+image: 'python:latest'
+
+# Run unittests
+test:
+    stage: test
+    tags:
+    - docker
+
+    script:
+      - pip install pytest-cov
+      - pip install .
+      - pytest --cov