t7800: update copyright notice

Signed-off-by: NDavid Aguilar <davvid@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

t/t7800-difftool.sh

 #!/bin/sh
 #
-# Copyright (c) 2009, 2010 David Aguilar
+# Copyright (c) 2009, 2010, 2012, 2013 David Aguilar
 #
 
 test_description='git-difftool