message: better channel mention typings. Remove undefined
diff: @@ -20,7 +20,7 @@ export function createMessage(data: MessageCreateOptions) {
  guildID: guildID || "",
  mentionsEveryone,
  mentionRoles,
  - mentionChannels,
  + mentionChannels: mentionChannels || [],
  webhookID,
  messageReference,
  timestamp: Date.parse(data.timestamp),
  