Visitor of dallas, and a Date of june 12 had what highest attendance?
CREATE TABLE "stanley_cup_final" (
  "date" text,
  "visitor" text,
  "score" text,
  "home" text,
  "decision" text,
  "attendance" real
);
SELECT MAX("attendance") FROM "stanley_cup_final" WHERE "visitor"='dallas' AND "date"='june 12';