travis: run pyqt5 tests on stable

Author: thocevar

.travis.yml

@@ -17,7 +17,6 @@ matrix:
           script: source $TRAVIS_BUILD_DIR/.travis/build_doc.sh
         - python: '3.5'
           env: PYQT5=true
-          dist: trusty
           addons: { apt: { packages: [] } }
     allow_failures:
         - *pylint