Travis-CI: set SPHINXOPTS="-W" for make docs

.travis.yml

@@ -1,54 +1,54 b''
 # http://travis-ci.org/#!/ipython/ipython
 language: python
 python:
     - "nightly"
     - 3.6
     - 3.5
     - 3.4
     - 3.3
 sudo: false
 env:
   global:
     - PATH=$TRAVIS_BUILD_DIR/pandoc:$PATH
 group: edge
 before_install:
     - 'if [[ $GROUP != js* ]]; then COVERAGE=""; fi'
 install:
     - pip install setuptools pip --upgrade
     - pip install -e file://$PWD#egg=ipython[test] --upgrade
     - pip install codecov --upgrade
     - sudo apt-get install graphviz
 script:
     - cd /tmp && iptest --coverage xml && cd -
     # On the latest Python only, make sure that the docs build.
     - |
       if [[ "$TRAVIS_PYTHON_VERSION" == "3.6" ]]; then
         pip install -r docs/requirements.txt
-        make -C docs/ html
+        make -C docs/ html SPHINXOPTS="-W"
       fi
 after_success:
     - cp /tmp/ipy_coverage.xml ./
     - cp /tmp/.coverage ./
     - codecov
 
 matrix:
     allow_failures:
         - python: nightly
 
 before_deploy:
     - rm -rf dist/
     - python setup.py sdist
     - python setup.py bdist_wheel
 
 deploy:
     provider: releases
     api_key:
         secure: Y/Ae9tYs5aoBU8bDjN2YrwGG6tCbezj/h3Lcmtx8HQavSbBgXnhnZVRb2snOKD7auqnqjfT/7QMm4ZyKvaOEgyggGktKqEKYHC8KOZ7yp8I5/UMDtk6j9TnXpSqqBxPiud4MDV76SfRYEQiaDoG4tGGvSfPJ9KcNjKrNvSyyxns=
     file: dist/*
     file_glob: true
     skip_cleanup: true
     on:
         repo: ipython/ipython
         all_branches: true  # Backports are released from e.g. 5.x branch
         tags: true
         python: 3.6  # Any version should work, but we only need one