package/domoticz: fix build with jsoncpp

domoticz embeds its own version of jsoncpp that can clash with upstream
jsoncpp so retrieve upstream commit that fix this issue

Build failures started after jsoncpp bumps from 1.8.4 to 1.9.1

Fixes:
 - http://autobuild.buildroot.org/results/a73406eb780a454369ea997654b6b4c6b3757a41



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>