Nixos unstable is changing the way sieve is configured in dovecot2 module

I believe this commit https://github.com/NixOS/nixpkgs/commit/1e31a631b7274886b009dc92f285e6d2a04662be is breaking SNM as it is for the moment.

Updating to it leads to:

Jan 14 19:48:39 captaincourier systemd[1]: Starting Dovecot IMAP/POP3 server...
Jan 14 19:48:39 captaincourier dovecot2-pre-start[21238]: after: line 1: error: require command: unknown Sieve capability `fileinto'.
Jan 14 19:48:39 captaincourier dovecot2-pre-start[21238]: after: line 4: error: unknown command 'fileinto' (only reported once at first oc>
Jan 14 19:48:39 captaincourier dovecot2-pre-start[21238]: after: error: validation failed.
Jan 14 19:48:39 captaincourier dovecot2-pre-start[21238]: sievec: Fatal: failed to compile sieve script '/var/lib/dovecot/sieve/after'