Fixed updating members without ManageNicknames

src/Discord.Net/API/Client/Rest/UpdateMember.cs

@@ -1,5 +1,6 @@
 using Discord.API.Converters;
 using Newtonsoft.Json;
+using System.ComponentModel;
 
 namespace Discord.API.Client.Rest
 {
@@ -21,7 +22,7 @@ namespace Discord.API.Client.Rest
         public ulong? VoiceChannelId { get; set; }
         [JsonProperty("roles"), JsonConverter(typeof(LongStringArrayConverter))]
         public ulong[] RoleIds { get; set; }
-        [JsonProperty("nick")]
+        [JsonProperty("nick", DefaultValueHandling = DefaultValueHandling.Ignore), DefaultValue("")]
         public string Nickname { get; set; }
 
         public UpdateMemberRequest(ulong guildId, ulong userId)