dejavu-fonts: update homepage

http://dejavu-fonts.org was taken over by an entity unrelated to the project

pkgs/data/fonts/dejavu-fonts/default.nix

···
       This package includes DejaVu Sans, DejaVu Serif, DejaVu Sans Mono, and
       the TeX Gyre DejaVu Math font.
     '';
-    homepage = "http://dejavu-fonts.org/wiki/Main_Page";
+    homepage = "https://dejavu-fonts.github.io/";
 
     # Copyright (c) 2003 by Bitstream, Inc. All Rights Reserved.
     # Copyright (c) 2006 by Tavmjong Bah. All Rights Reserved.