`Until` not in scope

[marcosh]

Running the following specification

import quickstrom;

let ~proposition = false until true;

check proposition with * when loaded?;

with the following command

docker run --rm -v $PWD:/spec quickstrom/quickstrom:0.5.0 quickstrom -I/spec check spec https://www.google.com

produces the following error

Check was aborted:

/spec/spec.strom:3:25: Variable not in scope: 
  _until_

Adding an import ltl;

produces the following error

Check was aborted:

/nix/store/xradz0aav0ijajw91x1vqfqsprgipfhx-specstrom/share/ulib/ltl.strom:1:1: syntax already declared:

[owickstrom]

Thanks for the nice bug report! Hoping I can find a moment to fix this soon. @liamoc might have some clue as to why this happens?