fix: correct tool name and copyright header in a plugin example code

tests/plugins/example/__init__.py

@@ -1,9 +1,20 @@
-#
+# -*- coding: utf-8 -*-
 # Copyright (C) 2020 Satoru SATOH
 #
-# SPDX-License-Identifier: GPL-3.0-or-later
+# 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.
 #
-"""YAML Lint plugin entry point
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+"""yamllint plugin entry point
 """
 from __future__ import absolute_import