Update copyright years

Using an interval 1996-2020.

Fixes: #9834

Author: xavierleroy

README.adoc

@@ -76,11 +76,10 @@ the compiler may work under other operating systems with little work.
 
 == Copyright
 
-All files marked "Copyright INRIA" in this distribution are copyright 1996,
-1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008,
-2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019
-Institut National de Recherche en Informatique et en Automatique (INRIA)
-and distributed under the conditions stated in file LICENSE.
+All files marked "Copyright INRIA" in this distribution are
+Copyright (C) 1996-2020 Institut National de Recherche en Informatique et
+en Automatique (INRIA) and distributed under the conditions stated in
+file LICENSE.
 
 == Installation