In 1994 what tournament held a ATP masters series
CREATE TABLE "doubles_performance_timeline" (
  "tournament" text,
  "1990" text,
  "1991" text,
  "1992" text,
  "1993" text,
  "1994" text,
  "1995" text,
  "1996" text,
  "1997" text,
  "1998" text,
  "career_sr" text
);
SELECT "1994" FROM "doubles_performance_timeline" WHERE "tournament"='atp masters series';