Pin Jedi to <0.17.2.

This may not completely fix the issue, in particular pip may decide to
downgrade IPython,  but maybe this will lead to less errors.

setup.py

@@ -186,7 +186,7 b' extras_require = dict('
 
 install_requires = [
     'setuptools>=18.5',
-    'jedi>=0.10',
+    'jedi>=0.10,<=0.17.2',
     'decorator',
     'pickleshare',
     'traitlets>=4.2',