refactor(Channel): make delete async (#6417)

src/structures/Channel.js

@@ -93,11 +93,9 @@ class Channel extends Base {
    *   .then(console.log)
    *   .catch(console.error);
    */
-  delete() {
-    return this.client.api
-      .channels(this.id)
-      .delete()
-      .then(() => this);
+  async delete() {
+    await this.client.api.channels(this.id).delete();
+    return this;
   }
 
   /**