Add TextChannel#setNSFW method (#2050)

* Add TextChannel#setNSFW method

* Doesn't look like anything to me

* butts

src/structures/TextChannel.js

@@ -38,6 +38,16 @@ class TextChannel extends GuildChannel {
     if (data.messages) for (const message of data.messages) this.messages.create(message);
   }
 
+  /**
+   * Sets whether this channel is flagged as NSFW.
+   * @param {boolean} nsfw Whether the channel should be considered NSFW
+   * @param {string} [reason] Reason for changing the channel's NSFW flag
+   * @returns {Promise<TextChannel>}
+   */
+  setNSFW(nsfw, reason) {
+    return this.edit({ nsfw }, reason);
+  }
+
   /**
    * Fetches all webhooks for the channel.
    * @returns {Promise<Collection<Snowflake, Webhook>>}