dmusic: Fix license headers that mistakenly use GPL instead of LGPL.

Confirmed by the original author and the major contributors.
diff --git a/include/dmusics.h b/include/dmusics.h
index 6baeab3..779b4c6 100644
--- a/include/dmusics.h
+++ b/include/dmusics.h
@@ -3,19 +3,19 @@
  *
  *  Copyright (C) 2003-2004 Rok Mandeljc
  *
- *  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 of the License, or
- *  (at your option) any later version.
+ *  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 2.1 of the License, or (at your option) any later version.
  *
  *  This program is distributed in the hope that it will be useful,
  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
- *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- *  GNU Library General Public License for more details.
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
  *
- *  You should have received a copy of the GNU General Public License
- *  along with this program; if not, write to the Free Software
- *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA.
+ *  You should have received a copy of the GNU Lesser General Public
+ *  License along with this program; if not, write to the Free Software
+ *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
  */
 
 #ifndef __WINE_DMUSIC_SOFTWARESYNTH_H