nixpkgs: use alacritty 0.6.0
nixpkgs: use alacritty 0.6.0

For whatever reason, using this version of alacritty makes `emacsclient
-t' run about 10x faster on startup. It's probably something to do with
tty/terminfo stuff, but we're too lazy to debug it.

listx/syscfg,listx/syscfg,listx/syscfg,listx/syscfg,listx/syscfg