ci: Travis: before_install for py34

Author: blueyed

.travis.yml

@@ -11,6 +11,11 @@ jobs:
       env: TOXENV=py27-coverage
     - python: '3.4'
       env: TOXENV=py34-coverage
+      before_install:
+        # Install latest available pip.
+        # 18.1 (installed) is too old to not install too new packages (attrs).
+        # 19.2 dropped support for Python 3.4.
+        - python -m pip install -U pip==19.1.1
     - python: '3.5'
       env: TOXENV=py35-coverage
     - python: '3.6'