[FIX] MANIFEST: add the mp3 file in manifest

Necessary to include the mp3 files in the rpm package

Closes #7352
Fixes #6356

MANIFEST.in

@@ -7,6 +7,7 @@ recursive-include openerp *.gif
 recursive-include openerp *.html
 recursive-include openerp *.jpeg
 recursive-include openerp *.jpg
+recursive-include openerp *.mp3
 recursive-include openerp *.js
 recursive-include openerp *.less
 recursive-include openerp *.md