Update license header

src/main/java/ladysnake/requiem/mixin/possession/player/HungerManagerMixin.java

@@ -1,3 +1,20 @@
+/*
+ * Requiem
+ * Copyright (C) 2019 Ladysnake
+ *
+ * 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 3 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <https://www.gnu.org/licenses>.
+ */
 package ladysnake.requiem.mixin.possession.player;
 
 import ladysnake.requiem.api.v1.RequiemPlayer;