error: can't find file InstaGibPlus9.

[Roemer]

Hello all
I am trying to add this mutator to my ut99 server docker image over at https://github.com/Roemer/ut99-server
but when I add it and also the config values ServerPackages InstaGibPlus9 and ServerActors InstaGibPlus9.NewNetServer and InstaGibPlus9.PureStats I get the following error on startup of the server:

Failed to load InstaGibPlus9: Can't find file InstaGibPlus9..

Am I missing something? Didn't see anything else in the server setup.