feat(GuildChannel): add fetchInvites method

Backported from commit: 47bc0fc51e
PR: #2339

src/structures/GuildChannel.js

@@ -4,6 +4,7 @@ const PermissionOverwrites = require('./PermissionOverwrites');
 const Permissions = require('../util/Permissions');
 const Collection = require('../util/Collection');
 const Constants = require('../util/Constants');
+const Invite = require('./Invite');
 
 /**
  * Represents a guild channel (i.e. text channels and voice channels).
@@ -332,6 +333,24 @@ class GuildChannel extends Channel {
       .then(channel => withTopic ? channel.setTopic(this.topic) : channel);
   }
 
+  /**
+   * Fetches a collection of invites to this guild channel.
+   * Resolves with a collection mapping invites by their codes.
+   * @returns {Promise<Collection<string, Invite>>}
+   */
+  fetchInvites() {
+    return this.client.rest.makeRequest('get', Constants.Endpoints.Channel(this.id).invites, true)
+      .then(data => {
+        const invites = new Collection();
+        for (let invite of data) {
+          invite = new Invite(this.client, invite);
+          invites.set(invite.code, invite);
+        }
+
+        return invites;
+      });
+  }
+
   /**
    * Deletes this channel.
    * @param {string} [reason] Reason for deleting this channel