Do not test against astroid (rhbz#2034943)
    
    In https://github.com/gristlabs/asttokens/issues/79, upstream says
    that astroid is only used optionally. It seems that our users of
    asttokens do not actually use it with astroid, but with plain ast, so
    the incompatiblity with newest astroid doesn't impact us.
    
    Let's skip the tests for now and hope that this will be resolved if
    somebody wants to use asttokens with astroid.