chore(.travis.yml): work around change in Travis OS X image
chore(.travis.yml): work around change in Travis OS X image


dselsam/lean,Kha/lean,digama0/lean,leanprover-community/lean,dselsam/lean,leanprover/lean,leanprover-community/lean,Kha/lean,dselsam/lean,digama0/lean,digama0/lean,Kha/lean,fpvandoorn/lean,leodemoura/lean,dselsam/lean,leodemoura/lean,leanprover/lean,fpvandoorn/lean,digama0/lean,dselsam/lean,digama0/lean,leodemoura/lean,digama0/lean,leanprover-community/lean,fpvandoorn/lean,fpvandoorn/lean,leanprover-community/lean,leanprover/lean,fpvandoorn/lean,Kha/lean,leanprover/lean,dselsam/lean,leodemoura/lean,fpvandoorn/lean,leodemoura/lean,Kha/lean,leodemoura/lean,leanprover/lean,Kha/lean,leanprover/lean,leanprover-community/lean,leanprover-community/lean