Update extensions in uploadFile for sendAudio

I have added the audio/mpeg mimetype for the sendAudio function, because Telegram only accepts .mp3 files up to 50 mb.

src/Telegram.php

@@ -492,6 +492,7 @@ private function uploadFile($method, $data)
         'image/bmp'   =>  '.bmp',
         'image/tiff'  =>  '.tif',
         'audio/ogg'   =>  '.ogg',
+        'audio/mpeg'  =>  '.mp3',
         'video/mp4'   =>  '.mp4',
         'image/webp'  =>  '.webp'
       );