fix(library/simplifier): compilation warning
fix(library/simplifier): compilation warning

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

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