set CXX environment variable instead of using update-alternatives. allows travis to use sudo-less containers which start in seconds.
set CXX environment variable instead of using update-alternatives. allows travis to use sudo-less containers which start in seconds.

fleg/nan,Jonekee/nan,sanemat/nan,nodejs/nan,thefourtheye/nan,guymguym/nan,ipmobiletech/nan,evanlucas/nan,nodejs/nan,mikolalysenko/nan,Jonekee/nan,sanemat/nan,lovell/nan,fleg/nan,saper/nan,LinusU/nan,lovell/nan,LinusU/nan,eljefedelrodeodeljefe/nan,addaleax/nan,gagern/nan,guymguym/nan,guymguym/nan,fleg/nan,lovell/nan,addaleax/nan,eljefedelrodeodeljefe/nan,fleg/nan,Jonekee/nan,durai145/nan,saper/nan,sanemat/nan,saper/nan,gagern/nan,eljefedelrodeodeljefe/nan,thefourtheye/nan,evanlucas/nan,ipmobiletech/nan,addaleax/nan,durai145/nan,sanemat/nan,sesh-kebab/nan,mikolalysenko/nan,sesh-kebab/nan,saper/nan,sesh-kebab/nan,eljefedelrodeodeljefe/nan,ipmobiletech/nan,mikolalysenko/nan,Jonekee/nan,durai145/nan,guymguym/nan,mikolalysenko/nan,LinusU/nan,mscdex/nan,mscdex/nan,sesh-kebab/nan,mscdex/nan,durai145/nan,LinusU/nan,mscdex/nan,nodejs/nan,lovell/nan,thefourtheye/nan,evanlucas/nan,addaleax/nan,gagern/nan,thefourtheye/nan,nodejs/nan,ipmobiletech/nan,evanlucas/nan