try install_egg_info workaround

suggested here: https://github.com/pypa/pip/issues/4537

.travis.yml

@@ -1,5 +1,5 @@
 language: python
-ython: 
+python: 
   - '3.8.3'
   - '3.7.7'
   - '3.6.10'
@@ -9,6 +9,7 @@ before_install:
   - python -m pip install --upgrade pip
   - pip install black pytest pytest-xdist --upgrade
 install:
+  - python setup.py install_egg_info
   - pip install -e .
   - pip freeze # print all pip packages & versions
 script: