CI: Pin IPYthon for doc build (#22991)

TomAugspurger · web-flow · commit f4dfcfd94266 · 2018-10-04T10:15:57.000-05:00
diff --git a/ci/travis-36-doc.yaml b/ci/travis-36-doc.yaml
@@ -12,7 +12,7 @@ dependencies:
   - html5lib
   - hypothesis>=3.58.0
   - ipykernel
-  - ipython
+  - ipython==6.5.0
   - ipywidgets
   - lxml
   - matplotlib
