@classmethod
def clean_env(cls, content: dict) ->dict:
    """
        Given the content of the Travis CI configuration file,
        we clean the env entries.
        """
    to_delete = ['matrix']
    if 'env' in content:
        for env_var in to_delete:
            if env_var in content['env']:
                del content['env'][env_var]
    return content
