force older astroid

.travis.yml

@@ -9,8 +9,9 @@ jobs:
     - stage: code quality
       name: "pylint & mypy"
       install:
-        - pip install git+https://github.com/PyCQA/pylint.git
+        - pip install astroid==2.0.4
-        - pip install mypy
+        # newer astroid fails in pylint so we pre-install older version
+        - pip install pylint mypy
         - pip install -e .
       script:
         - pylint --rcfile=setup.cfg torba