Do I need to get a noble in order to win Splendor?
No. From the rulebook, hosted on the creator's website, no mention of nobles as part of the win condition:


  END OF THE GAME
  
  When a player reaches 15 prestige points, complete the
  current round so that each player has played the same number
  of turns.
  The player who then has the highest number of prestige points
  is declared the winner (don’t forget to count your nobles).
  In case of a tie, the player who has purchased the fewest
  development cards wins.