fix(frontends/lean/parser): generate flycheck-friendly import error
fix(frontends/lean/parser): generate flycheck-friendly import error

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

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