Fix a minor grammar mistake

src/Discord.Net.Webhook/DiscordWebhookClient.cs

@@ -85,7 +85,7 @@ namespace Discord.Webhook
         }
         private static API.DiscordRestApiClient CreateApiClient(DiscordRestConfig config)
             => new API.DiscordRestApiClient(config.RestClientProvider, DiscordRestConfig.UserAgent);
-        /// <summary> Sends a message using to the channel for this webhook. </summary>
+        /// <summary> Sends a message to the channel for this webhook. </summary>
         /// <returns> Returns the ID of the created message. </returns>
         public Task<ulong> SendMessageAsync(string text = null, bool isTTS = false, IEnumerable<Embed> embeds = null,
             string username = null, string avatarUrl = null, RequestOptions options = null)