feat(lua): install Lua at travis VM
feat(lua): install Lua at travis VM

Signed-off-by: Leonardo de Moura <7610bae85f2b530654cc716772f1fe653373e892@microsoft.com>

c-cube/lean,eigengrau/lean,eigengrau/lean,Kha/lean,soonhokong/lean,avigad/lean,javra/lean,soonhokong/travis_test,leodemoura/lean,johoelzl/lean,htzh/lean,johoelzl/lean,levnach/lean,johoelzl/lean,c-cube/lean,digama0/lean,htzh/lean,UlrikBuchholtz/lean,dselsam/lean,rlewis1988/lean,soonhokong/lean-osx,fpvandoorn/lean2,leanprover-community/lean,Kha/lean,javra/lean,soonhokong/lean-windows,Kha/lean,soonhokong/lean-windows,soonhokong/lean-osx,fgdorais/lean,leanprover/lean,leanprover-community/lean,dselsam/lean,avigad/lean,c-cube/lean,codyroux/lean0.1,eigengrau/lean,sp3ctum/lean,fgdorais/lean,soonhokong/lean-osx,soonhokong/travis_test,levnach/lean,johoelzl/lean,eigengrau/lean,leanprover/lean,Kha/lean,soonhokong/lean,digama0/lean,leodemoura/lean,soonhokong/lean-windows,fpvandoorn/lean,rlewis1988/lean,avigad/lean,levnach/lean,fgdorais/lean,UlrikBuchholtz/lean,Kha/lean,digama0/lean,soonhokong/lean-windows,leanprover/lean,leanprover/lean,UlrikBuchholtz/lean,avigad/lean,soonhokong/lean-osx,rlewis1988/lean,johoelzl/lean,fpvandoorn/lean,leanprover-community/lean,soonhokong/travis_test,soonhokong/lean,javra/lean,levnach/lean,UlrikBuchholtz/lean,htzh/lean,fgdorais/lean,levnach/lean,Kha/lean,htzh/lean,dselsam/lean,c-cube/lean,soonhokong/lean,digama0/lean,fgdorais/lean,avigad/lean,fgdorais/lean,leodemoura/lean,sp3ctum/lean,codyroux/lean0.1,fpvandoorn/lean,sp3ctum/lean,rlewis1988/lean,digama0/lean,soonhokong/lean-osx,sp3ctum/lean,dselsam/lean,javra/lean,fpvandoorn/lean2,leodemoura/lean,leanprover/lean,UlrikBuchholtz/lean,avigad/lean,fpvandoorn/lean2,codyroux/lean0.1,soonhokong/travis_test,dselsam/lean,c-cube/lean,soonhokong/lean-windows,leanprover-community/lean,leodemoura/lean,htzh/lean,rlewis1988/lean,leanprover/lean,rlewis1988/lean,dselsam/lean,eigengrau/lean,leanprover-community/lean,fpvandoorn/lean2,digama0/lean,fpvandoorn/lean,sp3ctum/lean,fpvandoorn/lean,fpvandoorn/lean2,johoelzl/lean,fpvandoorn/lean,leodemoura/lean,soonhokong/lean,codyroux/lean0.1,javra/lean,leanprover-community/lean