Addition of required library missed in merge

src/Discord.Net.WebSocket/Entities/Interaction/Slash Commands/SocketSlashCommand.cs

@@ -1,6 +1,7 @@
 using Discord.Rest;
 using Newtonsoft.Json.Linq;
 using System;
+using System.Linq;
 using System.Threading.Tasks;
 using DataModel = Discord.API.ApplicationCommandInteractionData;
 using Model = Discord.API.Gateway.InteractionCreated;