Dynamically create PY3 version of the file by re-writing 'unicode' to 'str'.

def _preprocess_yml(path):
    """Dynamically create PY3 version of the file by re-writing 'unicode' to 'str'."""
    with open(path) as f:
        tmp_yaml = f.read()
    return re.sub(r"unicode", "str", tmp_yaml)