Update new file's license header

Author: LexManos

src/main/java/net/minecraftforge/launcher/FG2Hacks.java

@@ -1,23 +1,7 @@
 /*
- * A Gradle plugin for the creation of Minecraft mods and MinecraftForge plugins.
- * Copyright (C) 2013-2019 Minecraft Forge
- *
- * This library 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 library 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
- * Lesser General Public License for more details.
- *
- * You should have received a copy of the GNU Lesser General Public
- * License along with this library; if not, write to the Free Software
- * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301
- * USA
+ * Copyright (c) Forge Development LLC and contributors
+ * SPDX-License-Identifier: LGPL-2.1-only
  */
-
 package net.minecraftforge.launcher;
 
 import java.io.File;