debian: Amend copyright file

- Fix Upstream-Name and Source URL.
- Add Upstream-Contact.
- Fix LGPL's long name.
- Fix path to source file Invalid image.

debian/copyright

@@ -1,21 +1,22 @@
 Format: https://www.debian.org/doc/packaging-manuals/copyright-format/1.0/
-Upstream-Name: xapps
-Source: https://github.com/linuxmint/xapps
+Upstream-Name: xapp
+Upstream-Contact: https://www.linuxmint.com/teams.php
+Source: https://github.com/linuxmint/xapp
 
 Files: *
 Copyright: 2016, Linux Mint
-License: LGPL-3+
+License: LGPL-3
  This program is free software; you can redistribute it and/or
- modify it under the terms of the GNU Library General Public License V3.
+ modify it under the terms of the GNU Lesser General Public License V3.
  .
- The complete text of the GNU Library General Public License can be found in
- "/usr/share/common-licenses/LGPL-3".
+ The complete text of the GNU Lesser General Public License version 3 can be
+ found in "/usr/share/common-licenses/LGPL-3".
 
-Files: files/usr/bin/xfce4-set-wallpaper
+Files: scripts/xfce4-set-wallpaper
 Copyright: Weitian Leung <[email protected]>
 License: GPL-3
  This program is free software; you can redistribute it and/or
  modify it under the terms of the GNU General Public License V3.
  .
- The complete text of the GNU Library General Public License can be found in
+ The complete text of the GNU General Public License version 3 can be found in
  "/usr/share/common-licenses/GPL-3".