all: Fix license name

"GNU Public License" does not exist. It is called "GNU General Public
License", "GNU GPL" or simply "GPL".

Author: ikarienator

LICENSE.txt

@@ -1,6 +1,6 @@
 HIDAPI can be used under one of three licenses.
 
-1. The GNU Public License, version 3.0, in LICENSE-gpl3.txt
+1. The GNU General Public License, version 3.0, in LICENSE-gpl3.txt
 2. A BSD-Style License, in LICENSE-bsd.txt.
 3. The more liberal original HIDAPI license. LICENSE-orig.txt
 

hidapi/hidapi.h

@@ -11,7 +11,7 @@
 
  At the discretion of the user of this library,
  this software may be licensed under the terms of the
- GNU Public License v3, a BSD-Style license, or the
+ GNU General Public License v3, a BSD-Style license, or the
  original HIDAPI license as outlined in the LICENSE.txt,
  LICENSE-gpl3.txt, LICENSE-bsd.txt, and LICENSE-orig.txt
  files located at the root of the source distribution.

libusb/hid.c

@@ -14,7 +14,7 @@
 
  At the discretion of the user of this library,
  this software may be licensed under the terms of the
- GNU Public License v3, a BSD-Style license, or the
+ GNU General Public License v3, a BSD-Style license, or the
  original HIDAPI license as outlined in the LICENSE.txt,
  LICENSE-gpl3.txt, LICENSE-bsd.txt, and LICENSE-orig.txt
  files located at the root of the source distribution.

linux/hid.c

@@ -12,7 +12,7 @@
 
  At the discretion of the user of this library,
  this software may be licensed under the terms of the
- GNU Public License v3, a BSD-Style license, or the
+ GNU General Public License v3, a BSD-Style license, or the
  original HIDAPI license as outlined in the LICENSE.txt,
  LICENSE-gpl3.txt, LICENSE-bsd.txt, and LICENSE-orig.txt
  files located at the root of the source distribution.

mac/hid.c

@@ -11,7 +11,7 @@
 
  At the discretion of the user of this library,
  this software may be licensed under the terms of the
- GNU Public License v3, a BSD-Style license, or the
+ GNU General Public License v3, a BSD-Style license, or the
  original HIDAPI license as outlined in the LICENSE.txt,
  LICENSE-gpl3.txt, LICENSE-bsd.txt, and LICENSE-orig.txt
  files located at the root of the source distribution.

windows/hid.c

@@ -11,7 +11,7 @@
  
  At the discretion of the user of this library,
  this software may be licensed under the terms of the
- GNU Public License v3, a BSD-Style license, or the
+ GNU General Public License v3, a BSD-Style license, or the
  original HIDAPI license as outlined in the LICENSE.txt,
  LICENSE-gpl3.txt, LICENSE-bsd.txt, and LICENSE-orig.txt
  files located at the root of the source distribution.