package/python-django: security bump to version 3.0.3

package/python-django: security bump to version 3.0.3

Fixes the following security issues:

- CVE-2020-7471: Potential SQL injection via StringAgg(delimiter)
  django.contrib.postgres.aggregates.StringAgg aggregation function was
  subject to SQL injection, using a suitably crafted delimiter.

For more details, see the advisory:
https://www.djangoproject.com/weblog/2020/feb/03/security-releases/

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>