contrib: specify jsoncpp min version >= 1.6.5

Ubuntu still ships 0.10.5, so the contrib version should still be
used in that case.

Change-Id: I115cac27cab827367e92967a9fcb9cc8cfa29ccf
Tuleap: #597

contrib/src/jsoncpp/rules.mak

@@ -4,7 +4,7 @@ JSONCPP_URL := https://github.com/open-source-parsers/jsoncpp/archive/$(JSONCPP_
 
 PKGS += jsoncpp
 
-ifeq ($(call need_pkg,'jsoncpp'),)
+ifeq ($(call need_pkg,"jsoncpp >= 1.6.5"),)
 PKGS_FOUND += jsoncpp
 endif