python-cryptography: bump to version 1.2.3

Is now compatible with openssl 1.0.2g+ hence fixes:
http://autobuild.buildroot.net/results/5fc/5fc28bafa3cd7171ce6343d21f65af090536f443/



Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>