Strings with '%' symbols which aren't token placeholders don't format correctly

[lawmaestro]

For instance the following: "%s 0% fat Greek style yogurt" when formatted with: "60ml" should ideally result in: "60ml 0% fat Greek style yogurt" Instead the outcome is nil

I've taken a look over the code and this could be fixed by tweaking line 587 in Sprinter.swift: if first == "%" { break } to become:

if first == "%" {
  if string.last == nil || string.last == " " {
    break
  }
}

I've tested this locally and all unit tests pass with the change (as well as this new case). I'm happy to create a PR? Let me know, cheers.