feat: added MediaKey in order to see which sticker has been sent (#146)

src/structures/Message.js

@@ -17,6 +17,13 @@ class Message extends Base {
     }
 
     _patch(data) {
+        /**
+         * MediaKey that represents the sticker 'ID'
+         * @type {string}
+         */
+        this.mediaKey = data.mediaKey;
+
+
         /**
          * ID that represents the message
          * @type {object}