I ran:
$ raco pkg install lux
Resolving "lux" via http://download.racket-lang.org/releases/6.3/catalog/
Resolving "lux" via http://pkgs.racket-lang.org
Using cached15253002841525300284739 for git://github.com/jeapostrophe/lux
Promoting lux from auto-installed to explicitly installed
$ git clone https://gitlab.com/dustyweb/racktris.git