Update checkstyle.xml (2018 -> \d{4})
<!-- Copyright headers -->
<module name="RegexpSingleline">
- <property name="format" value="^ \* Copyright 2018 LINE Corporation$" />
+ <property name="format" value="^ \* Copyright \d{4} LINE Corporation$" />
<property name="minimum" value="1" />
<property name="maximum" value="1" />
<property name="message" value="missing copyright header" />
