cache: use latest file's time stamp instead of current time
cache: use latest file's time stamp instead of current time

bertfreudenberg/SqueakJS,bertfreudenberg/SqueakJS,the-impossible-quiz-revisited/the-impossible-quiz-revisited.github.io,Speed-Pad/online,sebastianconcept/SqueakJS,the-impossible-quiz-revisited/the-impossible-quiz-revisited.github.io,fmateoc/SqueakJS,sebastianconcept/SqueakJS,sebastianconcept/SqueakJS,fniephaus/SqueakJS,fmateoc/SqueakJS,fmateoc/SqueakJS,bertfreudenberg/SqueakJS,fniephaus/SqueakJS,the-impossible-quiz-revisited/the-impossible-quiz-revisited.github.io,Speed-Pad/online,fniephaus/SqueakJS,bertfreudenberg/SqueakJS,fmateoc/SqueakJS,the-impossible-quiz-revisited/the-impossible-quiz-revisited.github.io,Speed-Pad/online,fniephaus/SqueakJS