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

Backport PR #11477: pin pip on old python

.travis.yml

@@ -13,6 +13,12 @@ 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: