Added and fixed a bunch of docs stuff (#1767)

- Fixed a common copy paste fail `the the <thing>` in various places
- Apparently I can't type Resolvable correctly,
Fixed that wherever applicable
- Documented GroupDMChannel#nicks so that it will be displayed on the docs
- GroupDMChannel#icon is nullable
- Removed empty InviteOptions typdef, as its properties are now documented in GuildChannel#createInvite
- MessageMentions#channels is no longer nullable
- RoleData#permissions takes a PermissionResolvable or an array of them
- Webhook#avatar is nullable
- Added HTTPOptions typedef and added it to ClientOptions typedef
- ClientUserChannelOverride#muted is for a channel and not a guild directly

src/structures/GroupDMChannel.js

@@ -49,7 +49,7 @@ class GroupDMChannel extends Channel {
 
     /**
      * A hash of this Group DM icon
-     * @type {string}
+     * @type {?string}
      */
     this.icon = data.icon;
 
@@ -71,11 +71,13 @@ class GroupDMChannel extends Channel {
      */
     this.applicationID = data.application_id;
 
-    /**
-     * Nicknames for group members
-     * @type {?Collection<Snowflake, string>}
-     */
-    if (data.nicks) this.nicks = new Collection(data.nicks.map(n => [n.id, n.nick]));
+    if (data.nicks) {
+      /**
+       * Nicknames for group members
+       * @type {?Collection<Snowflake, string>}
+       */
+      this.nicks = new Collection(data.nicks.map(n => [n.id, n.nick]));
+    }
 
     if (!this.recipients) {
       /**
@@ -181,7 +183,7 @@ class GroupDMChannel extends Channel {
   /**
    * Adds an user to this Group DM.
    * @param {Object} options Options for this method
-   * @param {UserResolveable} options.user User to add to this Group DM
+   * @param {UserResolvable} options.user User to add to this Group DM
    * @param {string} [options.accessToken] Access token to use to add the user to this Group DM
    * (only available under a bot account)
    * @param {string} [options.nick] Permanent nickname to give the user (only available under a bot account)
@@ -198,7 +200,7 @@ class GroupDMChannel extends Channel {
 
   /**
    * Removes an user from this Group DM.
-   * @param {UserResolveable} user User to remove
+   * @param {UserResolvable} user User to remove
    * @returns {Promise<GroupDMChannel>}
    */
   removeUser(user) {