Fix update-doxygen (again)

Bash trickery to find the script directory did not work, but we can just use
"trunk/tools" since trunk gets checked out into $DOXYGEN_TEMPDIR.
Review URL: https://codereview.appspot.com/6573055

git-svn-id: http://skia.googlecode.com/svn/trunk@5696 2bbb7eff-a529-9590-31e7-b0007b416f81
1 file changed