Add fetch --prune to the sync?

[dragonpaw]

I feel like thematically, I'd really like it if legit sync also included fetch --prune since post-sync seeing branches that have actually been removed doesn't feel very 'synced' to me. (Otherwise I'm stuck always calling git sync; git fetch --prune and the main appeal of legit to me is to avoid having long git commands with a ton of options.)

(Yeah, I know I can alias this if I really want to.)