def transform_headers(headers):
    """
    Boto url-encodes values unless we convert the value to `str`, so doing
    this prevents 'max-age=100000' from being converted to "max-age%3D100000".

    :param headers: Headers to convert
    :type  headers: dict
    :rtype: dict

    """

    for key, value in headers.items():
        headers[key] = str(value)
    return headers