docplex config --upgrade fails when running within a venv

[Holt59]

If cplex and docplex are installed in a virtual environment (using the builtin venv module), docplex config --upgrade fails here: https://github.com/IBMDecisionOptimization/docplex/blob/master/docplex/util/cli.py#L55-L74

Replacing

out = subprocess.run(["python", "-c", sub_program], capture_output=True)

by

out = subprocess.run([sys.executable, "-c", sub_program], capture_output=True)

...seems to fix the issue.