debian: minor lintian fixes

Bump Standards-Version
Mark GPL-2+ license paragraph

Signed-off-by: Keith Packard <keithp@keithp.com>

debian/control

@@ -4,7 +4,7 @@ Priority: optional
 Maintainer: Keith Packard <keithp@keithp.com>
 Homepage: https://keithp.com
 Build-Depends: debhelper (>= 11), libreadline-dev, avr-libc, gcc-avr, python3, lola, gawk, asciidoctor, ruby-asciidoctor-pdf
-Standards-Version: 4.2.1
+Standards-Version: 4.3.0
 
 Package: snek
 Architecture: all

debian/copyright

@@ -6,7 +6,7 @@ Files: *
 Copyright: 2018-2019 Keith Packard
 License: GPL-2+
 
-License: 
+License: GPL-2+
  This program is free software; you can redistribute it and/or
  modify it under the terms of the GNU General Public License
  as published by the Free Software Foundation, either version 2