Merge pull request #3128 from takluyver/i3127

Pin to ipykernel 4.6.1 on Python 2 to avoid kernelspec issue

.travis.yml

@@ -4,6 +4,7 @@ language: python
 cache:
     directories:
         - $HOME/.cache/bower
+        - $HOME/.cache/pip
 python:
     - 3.6
     - 2.7
@@ -42,10 +43,16 @@ before_install:
 
 install:
     - pip install -f travis-wheels/wheelhouse file://$PWD#egg=notebook[test]
+    - |
+      if [[ "$TRAVIS_PYTHON_VERSION" == "2.7" ]]; then
+        # Work around https://github.com/ipython/ipykernel/issues/288
+        pip install ipykernel==4.6.1
+      fi
     - wget https://github.com/jgm/pandoc/releases/download/1.19.1/pandoc-1.19.1-1-amd64.deb && sudo dpkg -i pandoc-1.19.1-1-amd64.deb
 
 
 script:
+    - jupyter kernelspec list
     - 'if [[ $GROUP == js* ]]; then travis_retry python -m notebook.jstest ${GROUP:3}; fi'
     - 'if [[ $GROUP == python ]]; then nosetests -v --with-coverage --cover-package=notebook notebook; fi'
     - |