Travis CI failing on test_interactive_backend[qt5cairo] #11554
Description
Bug report
Travis CI tests are all failing on test_interactive_backend[qt5cairo]. i.e. https://travis-ci.org/matplotlib/matplotlib/jobs/399224639
I think...
ImportError: Matplotlib qt-based backends require an external PyQt4, PyQt5,
PySide or PySide2 package to be installed, but it was not found.