force Orange version to the latest compatible with python 3.5. Since 3.20 need python 3.6

.gitlab-ci.yml

@@ -13,7 +13,7 @@ test:python3.5-stretch-pyqt5:
     - python -m pip install setuptools --upgrade
     - python -m pip install numpy --upgrade
     - python -m pip install matplotlib
-    - python -m pip install Orange3
+    - python -m pip install Orange3==3.19.0
     - python -m pip install -r requirements.txt
     - python -m pip install .
     - /usr/bin/xvfb-run --server-args="-screen 0 1024x768x24" -a id06workflow test -v