fix(library/unifier): simple bug
fix(library/unifier): simple bug

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

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