package/python-django: security bump to version 2.1.10

Fixes the following security vulnerabilities:

CVE-2019-12781: Incorrect HTTP detection with reverse-proxy connecting via
HTTPS

For more details, see the announcement:
https://www.djangoproject.com/weblog/2019/jul/01/security-releases/



Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>