send uploaded_at as an iso-format date string

server/djrandom/model/mp3.py

@@ -77,7 +77,7 @@ class MP3(Base):
                 'genre': self.genre,
                 'sha1': self.sha1,
                 'size': self.size,
-                'uploaded_at': self.uploaded_at}
+                'uploaded_at': self.uploaded_at.isoformat()}
         if self.duplicate_of:
             data['duplicate_of'] = self.duplicate_of
         if self.track_num: