[ci skip] add missing final newline (PaperMC#8659)

Author: Machine-Maker

licenses/GPL.md

@@ -672,4 +672,4 @@ program into proprietary programs. If your program is a subroutine
 library, you may consider it more useful to permit linking proprietary
 applications with the library. If this is what you want to do, use the
 GNU Lesser General Public License instead of this License. But first,
-please read <https://www.gnu.org/licenses/why-not-lgpl.html>.
+please read <https://www.gnu.org/licenses/why-not-lgpl.html>.