Convert from unix timestamp to GMT string
    :param value:  unix timestamp
    :return: string with GMT time

def datetime(value):
    """
    Convert from unix timestamp to GMT string
    :param value:  unix timestamp
    :return: string with GMT time
    """
    if isinstance(value, (date, builtin_datetime)):
        pass
    elif value < 10000000000:
        value = unix2datetime(value)
    else:
        value = milli2datetime(value)

    return datetime2string(value, "%Y-%m-%d %H:%M:%S.%f").rstrip(".000000").rstrip("000")