Merge pull request #11478 from Carreau/auto-backport-of-pr-11477-on-5.x

Backport PR  #11477: pin pip on old python

.travis.yml

@@ -1,46 +1,52 b''
 # http://travis-ci.org/#!/ipython/ipython
 language: python
 python:
     - "nightly"
     - 3.6
     - 3.5
     - 3.4
     - 3.3
     - 2.7
     - pypy
 sudo: false
 before_install:
     - git clone --quiet --depth 1 https://github.com/minrk/travis-wheels travis-wheels
     - 'if [[ $GROUP != js* ]]; then COVERAGE=""; fi'
 install:
+    - |
+      if [[ "$TRAVIS_PYTHON_VERSION" == "3.3" ]]; then
+        pip install 'pip<18' --upgrade
+      else
+        pip install pip --upgrade
+      fi
     - pip install pip --upgrade
     - pip install "setuptools>=18.5" 
     # Installs PyPy (+ its Numpy). Based on @frol comment at:
     # https://github.com/travis-ci/travis-ci/issues/5027
     - |
         if [ "$TRAVIS_PYTHON_VERSION" = "pypy" ]; then
           export PYENV_ROOT="$HOME/.pyenv"
           if [ -f "$PYENV_ROOT/bin/pyenv" ]; then
             cd "$PYENV_ROOT" && git pull
           else
             rm -rf "$PYENV_ROOT" && git clone --depth 1 https://github.com/yyuu/pyenv.git "$PYENV_ROOT"
           fi
           export PYPY_VERSION="5.3.1"
           "$PYENV_ROOT/bin/pyenv" install "pypy-$PYPY_VERSION"
           virtualenv --python="$PYENV_ROOT/versions/pypy-$PYPY_VERSION/bin/python" "$HOME/virtualenvs/pypy-$PYPY_VERSION"
           source "$HOME/virtualenvs/pypy-$PYPY_VERSION/bin/activate"
           pip install https://bitbucket.org/pypy/numpy/get/master.zip
         fi
     - pip install -f travis-wheels/wheelhouse -e file://$PWD#egg=ipython[test]
     - pip install codecov mock
 script:
     - cd /tmp && iptest --coverage xml && cd -
 after_success:
     - cp /tmp/ipy_coverage.xml ./
     - cp /tmp/.coverage ./
     - codecov
 
 matrix:
     allow_failures:
         - python: nightly
         - python: pypy