Please downgrade keydb to 6.3.3

[sergiodj]

Hi,

keydb is currently affected by Snapchat/KeyDB#802 and can fail to start on some machines (mine included) when using the latest version 6.3.4. I have checked that version 6.3.3 works fine, and I'm manually downgrading the image for now, but I believe this should be done officially because other people might be impacted by this problem and it's a bit tricky to determine its root cause.

Thanks.