Nix: variables starting with reserved keywords are highlighted incorrectly

[UlyssesZh]

Name of the lexer Nix

Code sample

let
  if' = -1;
  trueTest = 1;
  falseTest = 0;
in { }

https://rouge.jneen.net/v4.6.1/nix/bGV0CiAgaWYnID0gLTE7CiAgdHJ1ZVRlc3QgPSAxOwogIGZhbHNlVGVzdCA9IDA7CmluIHsgfQ

Additional context