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

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

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