Revert back to gcc-4.8 for travis-ci
Revert back to gcc-4.8 for travis-ci

hanbinhu/libcds,xinghuwang/libcds,goswamia/libcds,Rapotkinnik/libcds,xinghuwang/libcds,Rapotkinnik/libcds,eugenyk/libcds,xinghuwang/libcds,eugenyk/libcds,Rapotkinnik/libcds,goswamia/libcds,goswamia/libcds,goswamia/libcds,hanbinhu/libcds,eugenyk/libcds,hanbinhu/libcds,hanbinhu/libcds,hanbinhu/libcds,elventear/libcds,eugenyk/libcds,elventear/libcds,elventear/libcds,eugenyk/libcds,goswamia/libcds,elventear/libcds,elventear/libcds,xinghuwang/libcds,Rapotkinnik/libcds,Rapotkinnik/libcds,xinghuwang/libcds