docs/typings(VoiceStateStore): document and type the class (#3294)

* Update index.d.ts

* Update Guild.js

* Update Guild.js

* docs/typings(VoiceStateStore): document and add typings

src/stores/VoiceStateStore.js

@@ -3,6 +3,10 @@
 const DataStore = require('./DataStore');
 const VoiceState = require('../structures/VoiceState');
 
+/**
+ * Stores voice states.
+ * @extends {DataStore}
+ */
 class VoiceStateStore extends DataStore {
   constructor(guild, iterable) {
     super(guild.client, iterable, VoiceState);

src/structures/Guild.js

@@ -57,6 +57,10 @@ class Guild extends Base {
      */
     this.presences = new PresenceStore(this.client);
 
+    /**
+     * A collection of voice states in this guild
+     * @type {VoiceStateStore<Snowflake, VoiceState>}
+     */
     this.voiceStates = new VoiceStateStore(this);
 
     /**