fix(kernel/expr): typo
fix(kernel/expr): typo

closes #1350

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