Update chart dependencies (#867)

charts/graylog/Chart.lock

charts/graylog/Chart.yaml

charts/graylog/README.md

charts/graylog/RELEASENOTES.md

charts/graylog/charts/mongodb-0.3.10.tgz

charts/graylog/charts/mongodb-0.3.9.tgz

charts/nextcloud/Chart.lock

charts/nextcloud/Chart.yaml

charts/nextcloud/README.md

charts/nextcloud/RELEASENOTES.md

charts/nextcloud/charts/mariadb-0.2.17.tgz

charts/nextcloud/charts/mariadb-0.2.18.tgz

charts/nextcloud/charts/postgres-0.2.16.tgz

charts/nextcloud/charts/postgres-0.2.17.tgz

charts/wordpress/Chart.lock

charts/wordpress/Chart.yaml

charts/wordpress/README.md

charts/wordpress/RELEASENOTES.md

charts/wordpress/charts/mariadb-0.2.17.tgz

charts/wordpress/charts/mariadb-0.2.18.tgz