try create venv to solve problem

.gitlab-ci.yml

@@ -96,7 +96,8 @@ tests:
     - chmod +x ./CI/update_badge.sh
     - ./CI/update_badge.sh > /dev/null
   script:
-    - pip install six==1.15.0
+    - python3.6 -m venv venv/
+    - source venv/bin/activate
     - pip install -r requirements.txt
     - chmod +x ./CI/run_pytest.sh
     - ./CI/run_pytest.sh
@@ -121,7 +122,6 @@ coverage:
     - chmod +x ./CI/update_badge.sh
     - ./CI/update_badge.sh > /dev/null
   script:
-    - pip install six==1.15.0
     - pip install -r requirements.txt
     - chmod +x ./CI/run_pytest_coverage.sh
     - ./CI/run_pytest_coverage.sh
@@ -144,7 +144,6 @@ sphinx docs:
     - chmod +x ./CI/update_badge.sh
     - ./CI/update_badge.sh > /dev/null
   script:
-    - pip install six==1.15.0
     - pip install -r requirements.txt
     - pip install -r docs/requirements_docs.txt
     - chmod +x ./CI/create_documentation.sh