fix(util/optional): move constructor
fix(util/optional): move constructor

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

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