drawutils: fix copyright

git blame:
    423 Nicolas George
     86 Stefano Sabatini
     19 Michael Niedermayer
      1 Reimar Döffinger

Initial commit:
commit bcfd9e82
Author: Stefano Sabatini <stefano.sabatini-lala@poste.it>
Date:   Sun Feb 20 23:42:17 2011 +0100

    lavfi: add drawutils

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>