package/paho-mqtt-c: security bump to version 1.3.9

Old security issue not fixed:
https://github.com/eclipse/paho.mqtt.c/issues/1084

https://github.com/eclipse/paho.mqtt.c/milestone/16?closed=1



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>