Update oss-parent to version 9

Signed-off-by: Sebastian Hoß <mail@shoss.de>
Added gpg-plugin configuration. Fixes #1 since the default value for
'useAgent' is true in newer versions of the plugin

Signed-off-by: Sebastian Hoß <mail@shoss.de>
update semantic versioning enforcer rule to version 0.9.18

Signed-off-by: Sebastian Hoß <mail@shoss.de>