Missing 9% VAT tax tariff

[BobKrusemeijer]

The Enum value of TaxClass is missing the new tax tariff of 9% which in effect since 1 January 2019. Could you please expand this enum class to contain this tariff as currently we get the wrong reports as result of this issue.

See:
https://github.com/paynl/csharp-sdk/blob/master/PAYNLSDK/Enums/enums.cs

  /// <summary>
    /// TaxClass enumeration
    /// </summary>
    public enum TaxClass
    {
        [EnumMember(Value = "N")]
        None = 0,
        [EnumMember(Value = "L")]
        Low = 6,
        [EnumMember(Value = "H")]
        High = 21
    }