Merge pull request #206 from duyaokun/fix-compile-cjson-error

Fixed compilation error in src/cjson.c observed in Visual Studio 2013.

This problem didn't cause breakage on any other platform, but this change should have been present anyway.

(cherry picked from commit dd2968f21e641945026db4bbdf02b3c13f833d74)
Signed-off-by: Bruce A. Mah <bmah@es.net>