chore(.travis.yml): disable BOOST build
chore(.travis.yml): disable BOOST build

leanprover/lean,Kha/lean,fpvandoorn/lean,avigad/lean,rlewis1988/lean,fpvandoorn/lean,leodemoura/lean,leodemoura/lean,dselsam/lean,digama0/lean,leanprover/lean,Kha/lean,johoelzl/lean,fgdorais/lean,rlewis1988/lean,rlewis1988/lean,avigad/lean,fgdorais/lean,leanprover-community/lean,digama0/lean,leanprover/lean,fpvandoorn/lean,avigad/lean,leanprover/lean,dselsam/lean,Kha/lean,leodemoura/lean,dselsam/lean,dselsam/lean,fpvandoorn/lean,fgdorais/lean,leanprover-community/lean,leodemoura/lean,johoelzl/lean,rlewis1988/lean,fpvandoorn/lean,digama0/lean,johoelzl/lean,leanprover/lean,leanprover-community/lean,digama0/lean,digama0/lean,johoelzl/lean,leodemoura/lean,avigad/lean,avigad/lean,johoelzl/lean,dselsam/lean,Kha/lean,fgdorais/lean,leanprover-community/lean,johoelzl/lean,Kha/lean,digama0/lean,leodemoura/lean,rlewis1988/lean,rlewis1988/lean,Kha/lean,avigad/lean,fgdorais/lean,leanprover-community/lean,fgdorais/lean,leanprover-community/lean,dselsam/lean,fpvandoorn/lean,leanprover/lean