fix(frontends/lean/parser): bug when parsing identifiers
fix(frontends/lean/parser): bug when parsing identifiers

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

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