fix numeric locale

In some locales (e.g. de_DE) floats have commas instead of
dots, but JSON requires dots.
See:
  https://github.com/open-source-parsers/jsoncpp/pull/9
  https://github.com/open-source-parsers/jsoncpp/pull/3

src/lib_json/json_writer.cpp

@@ -77,7 +77,7 @@ std::string valueToString(double value) {
 #else
   snprintf(buffer, sizeof(buffer), "%.16g", value);
 #endif
-
+  fixNumericLocale(buffer, buffer + strlen(buffer));
   return buffer;
 }