fix(kernel/environment): warning produced by clang
fix(kernel/environment): warning produced by clang

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

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