* Update Release note and prepare 1.9.4 release This PR updates release notes and prepare 1.9.4 release Signed-off-by: Yong Tang <yong.tang.github@outlook.com> * Remove spaces Signed-off-by: Yong Tang <yong.tang.github@outlook.com> * Add additional note for header plugin change. Signed-off-by: Yong Tang <yong.tang.github@outlook.com> Signed-off-by: Yong Tang <yong.tang.github@outlook.com>