MINIFI-34 - Add Travis badge to README.md
MINIFI-34 - Add Travis badge to README.md

This closes #17.

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

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