notification: relicense from LGPLv3 to LGPLv2

With the permission of Erick Pérez Castellanos <erick.red@gmail.com>,
the original author.

https://bugzilla.gnome.org/show_bug.cgi?id=673073

libgd/gd-notification.c

@@ -9,7 +9,7 @@
  *
  * This program is free software: you can redistribute it and/or modify it
  * under the terms of the GNU Lesser General Public License as published
- * by the Free Software Foundation, either version 3 of the License, or
+ * by the Free Software Foundation, either version 2 of the License, or
  * (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful, but

libgd/gd-notification.h

@@ -9,7 +9,7 @@
  *
  * This program is free software: you can redistribute it and/or modify it
  * under the terms of the GNU Lesser General Public License as published
- * by the Free Software Foundation, either version 3 of the License, or
+ * by the Free Software Foundation, either version 2 of the License, or
  * (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful, but