MINIFI-286: Fix compilcation error when GCC version is greater than 4.9
MINIFI-286: Fix compilcation error when GCC version is greater than 4.9

This closes #88.

Signed-off-by: Aldrin Piri <8746015474cd01110181ed51735247560fd08de4@apache.org>

benqiu2016/nifi-minifi-cpp,NiFiLocal/nifi-minifi-cpp,NiFiLocal/nifi-minifi-cpp,kevdoran/nifi-minifi-cpp,kevdoran/nifi-minifi-cpp,benqiu2016/nifi-minifi-cpp,brosander/nifi-minifi-cpp,dtrodrigues/nifi-minifi-cpp,brosander/nifi-minifi-cpp,minifirocks/nifi-minifi-cpp,phrocker/nifi-minifi-cpp,kevdoran/nifi-minifi-cpp,achristianson/nifi-minifi-cpp,apiri/nifi-minifi-cpp,jdye64/nifi-minifi-cpp,reynoldsjohn/nifi-minifi-cpp,benqiu2016/nifi-minifi-cpp,reynoldsjohn/nifi-minifi-cpp,minifirocks/nifi-minifi-cpp,phrocker/nifi-minifi-cpp,apiri/nifi-minifi-cpp,jdye64/nifi-minifi-cpp,kevdoran/nifi-minifi-cpp,reynoldsjohn/nifi-minifi-cpp,kevdoran/nifi-minifi-cpp,achristianson/nifi-minifi-cpp,dtrodrigues/nifi-minifi-cpp,jdye64/nifi-minifi-cpp,apiri/nifi-minifi-cpp,minifirocks/nifi-minifi-cpp,NiFiLocal/nifi-minifi-cpp,dtrodrigues/nifi-minifi-cpp,apiri/nifi-minifi-cpp,phrocker/nifi-minifi-cpp,achristianson/nifi-minifi-cpp,jdye64/nifi-minifi-cpp,phrocker/nifi-minifi-cpp,dtrodrigues/nifi-minifi-cpp,minifirocks/nifi-minifi-cpp,phrocker/nifi-minifi-cpp,dtrodrigues/nifi-minifi-cpp,apiri/nifi-minifi-cpp,jdye64/nifi-minifi-cpp,NiFiLocal/nifi-minifi-cpp,achristianson/nifi-minifi-cpp,brosander/nifi-minifi-cpp