Setup Travis-CI macOS for wheel building

def ci_macos():
    """
    Setup Travis-CI macOS for wheel building
    """
    run_command("brew install $PYTHON pipenv || echo \"Installed PipEnv\"")
    command_string = "sudo -H $PIP install "
    for element in DEPENDENCIES + REQUIREMENTS + ["-U"]:
        command_string += element + " "
    run_command(command_string)
    # Build a wheel
    run_command("sudo -H $PYTHON setup.py bdist_wheel")
    assert check_wheel_existence()
    exit(0)