Add isGif to message._patch (#963)

* Update Message.js

Add isGif to the message data

* add typings

Co-authored-by: Rajeh Taher <rajeh@reforward.dev>
Co-authored-by: Pedro Lopez <pedroslopez@me.com>

index.d.ts

@@ -525,6 +525,8 @@ declare namespace WAWebJS {
         broadcast: boolean,
         /** Indicates if the message was a status update */
         isStatus: boolean,
+        /** Indicates if the message is a Gif */
+        isGif: boolean,
         /** ID for the Chat that this message was sent to, except if the message was sent by the current user */
         from: string,
         /** Indicates if the message was sent by the current user */