trying to fix weird issue where cvxopt isn't installing properly

Author: pavelkomarov

.github/workflows/test.yml

@@ -16,6 +16,7 @@ jobs:
           python-version: '3.x'
       - name: tests and coverage
         run: |
+          pip install --upgrade pip setuptools wheel
           pip install -e .[advanced,dev] coveralls
           coverage run --source=pynumdiff --omit='pynumdiff/_version.py,pynumdiff/tests/*,pynumdiff/utils/old_pi_cruise_control.py' -m pytest -s
           coverage xml