Remove pipenv before running tests

.gitlab-ci.yml

@@ -8,6 +8,7 @@ run-tests:
   stage: testing
   script:
     - pip install --upgrade pip pipenv
+    - pipenv --rm
     - pipenv run pip install -e '.[tests]'
     - pipenv run ./run-tests.sh
   coverage: /TOTAL.*? (100(?:\.0+)?\%|[1-9]?\d(?:\.\d+)?\%)$/