Determine if this is an ASCII based data stream, simply by checking the bytes for the word 'solid'.

def _is_ascii_stl(first_bytes):
    """
    Determine if this is an ASCII based data stream, simply by checking the bytes for the word 'solid'.
    """
    is_ascii = False
    if 'solid' in first_bytes.decode("utf-8").lower():
        is_ascii = True

    return is_ascii