Fix 'curl: unknown --write-out variable' for .zip modpacks

[avionix-g]

I ran into this bug when trying to use the MODPACK envar. Example log:

[init] Running as uid=1000 gid=1000 with /data as 'drwxrwxr-x 9 1000 1000 4096 Sep 24 04:41 /data'
[init] Resolved version given latest into 1.17.1
[init] Resolving type given FABRIC
curl: unknown --write-out variable: 'effective_url'
[init] ERROR Invalid URL given for MODPACK:  resolved from https://gitlab.com/avionix/minecraft-mods/-/jobs/artifacts/master/raw/ueg-modpack-server.zip?job=ueg
[init]       Must be HTTP, HTTPS or FTP and a ZIP file

It seems to be a one-line fix (a typo in a curl variable). I've tested the fix locally and it works as expected.

[itzg]

Thanks!