alacritty: increase contrast
alacritty: increase contrast

This is the Tango theme as defined on the [alacritty
wiki](https://github.com/alacritty/alacritty/wiki/Color-schemes), with a
few exceptions:
 - use darker normal black, and use the same colour as background
 - use bright their white colour as foreground, and use pure white as
 bright white

paretje/dotfiles,paretje/dotfiles,paretje/dotfiles,paretje/dotfiles,paretje/dotfiles