Fixed encoding error when requesting members

src/Discord.Net/API/Gateway/RequestMembersParams.cs

@@ -13,7 +13,7 @@ namespace Discord.API.Gateway
         public int Limit { get; set; }
 
         [JsonProperty("guild_id")]
-        private ulong[] _guildIds;
+        private ulong[] _guildIds { get; set; }
         public IEnumerable<ulong> GuildIds { set { _guildIds = value.ToArray(); } }
         public IEnumerable<IGuild> Guilds { set { _guildIds = value.Select(x => x.Id).ToArray(); } }
     }