[fix] csv results filename encoding

searx/webapp.py

             csv.writerow([row.get(key, '') for key in keys])
         csv.stream.seek(0)
         response = Response(csv.stream.read(), mimetype='application/csv')
-        cont_disp = 'attachment;Filename=searx_-_{0}.csv'.format(search.query)
+        cont_disp = 'attachment;Filename=searx_-_{0}.csv'.format(search.query.encode('utf-8'))
         response.headers.add('Content-Disposition', cont_disp)
         return response
     elif search.request_data.get('format') == 'rss':