authors: Add Josh Matthews to AUTHORS

Author: pcwalton

AUTHORS.txt

@@ -17,6 +17,7 @@ Jason Orendorff <jorendorff@mozilla.com>
 Jeff Balogh <jbalogh@mozilla.com>
 Jeff Muizelaar <jmuizelaar@mozilla.com>
 Jeffrey Yasskin <jyasskin@gmail.com>
+Josh Matthews <josh@joshmatthews.net>
 Kelly Wilson <wilsonk@cpsc.ucalgary.ca>
 Lindsey Kuper <lkuper@mozilla.com>
 Marijn Haverbeke <marijnh@gmail.com>