feat(.travis.yml): use g++-4.9 on Travis
feat(.travis.yml): use g++-4.9 on Travis

soonhokong/lean,eigengrau/lean,soonhokong/lean-osx,avigad/lean,sp3ctum/lean,soonhokong/lean-windows,javra/lean,leodemoura/lean,leanprover/lean,htzh/lean,sp3ctum/lean,htzh/lean,johoelzl/lean,leanprover/lean,johoelzl/lean,leanprover/lean,Kha/lean,leanprover-community/lean,fpvandoorn/lean,fpvandoorn/lean2,avigad/lean,dselsam/lean,fgdorais/lean,fpvandoorn/lean,javra/lean,leodemoura/lean,htzh/lean,eigengrau/lean,soonhokong/lean,soonhokong/lean-osx,c-cube/lean,soonhokong/lean-windows,c-cube/lean,UlrikBuchholtz/lean,eigengrau/lean,levnach/lean,eigengrau/lean,Kha/lean,htzh/lean,fpvandoorn/lean2,dselsam/lean,fpvandoorn/lean2,leanprover-community/lean,sp3ctum/lean,fgdorais/lean,leanprover/lean,soonhokong/lean-windows,sp3ctum/lean,UlrikBuchholtz/lean,digama0/lean,dselsam/lean,levnach/lean,soonhokong/lean-osx,soonhokong/lean,rlewis1988/lean,johoelzl/lean,leanprover-community/lean,c-cube/lean,rlewis1988/lean,leodemoura/lean,soonhokong/lean,fpvandoorn/lean,dselsam/lean,fpvandoorn/lean,digama0/lean,johoelzl/lean,leanprover/lean,leodemoura/lean,leodemoura/lean,javra/lean,avigad/lean,UlrikBuchholtz/lean,levnach/lean,c-cube/lean,leanprover-community/lean,leanprover/lean,fpvandoorn/lean2,avigad/lean,sp3ctum/lean,fgdorais/lean,Kha/lean,johoelzl/lean,fpvandoorn/lean2,javra/lean,Kha/lean,fgdorais/lean,fpvandoorn/lean,digama0/lean,Kha/lean,fgdorais/lean,soonhokong/lean,UlrikBuchholtz/lean,rlewis1988/lean,digama0/lean,javra/lean,avigad/lean,UlrikBuchholtz/lean,rlewis1988/lean,rlewis1988/lean,digama0/lean,htzh/lean,c-cube/lean,dselsam/lean,avigad/lean,levnach/lean,levnach/lean,johoelzl/lean,soonhokong/lean-windows,soonhokong/lean-osx,eigengrau/lean,leanprover-community/lean,fpvandoorn/lean,fgdorais/lean,dselsam/lean,leanprover-community/lean,Kha/lean,soonhokong/lean-osx,rlewis1988/lean,leodemoura/lean,soonhokong/lean-windows,digama0/lean