Attempt to fix Travis failures with Python 3.7.x

Author: evogytis

.travis.yml

@@ -10,7 +10,9 @@ python:
   - "3.8-dev"  # 3.8 development branch
 
 install:
+  - pip install -U setuptools importlib-metadata
   - pip install -r requirements.txt
   - pip install .
+  
 script: 
   - pytest ./tests/testsuite.py