chore(library/vm/vm): fix gcc 4.8 warning
chore(library/vm/vm): fix gcc 4.8 warning

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