Fix /var/lib/mysql volume mount point

[ebeigarts]

Mariadb uses/var/lib/mysql and not /var/lib/mariadb

After upgrading, users will need to manually copy /var/lib/docker/volumes/../_data to /var/lib/dokku/services/mariadb/<app>/data.

You can get the current mount points using docker inspect .

"Mounts": [
    {
        "Source": "/var/lib/dokku/services/mariadb/<app>",
        "Destination": "/var/lib/mariadb",
        "Mode": "",
        "RW": true
    },
    {
        "Name": "51fe99a1645ad115a5dcf99e9e4805bbea8d9c07147f3144a0677275fca412b5",
        "Source": "/var/lib/docker/volumes/51fe99a1645ad115a5dcf99e9e4805bbea8d9c07147f3144a0677275fca412b5/_data",
        "Destination": "/var/lib/mysql",
        "Driver": "local",
        "Mode": "",
        "RW": true
    }
]

[Flink]

:+1: