Fixed an error in chapter 3

As I was working on chapter 15, changing it from a draft to a proper chapter, I realized I made a serious error in the early chapters. I do blame it on the fact that chapter 3 was actually written two years ago and I never got around to fix that small error.

Basically it's when Flash is reporting to Twilight on Sombra sightings, he was supposed to be vaguer about when the last possible sighting was and when the mountain goats were rescued by the yaks, I had actually long since decided it hadn't been that long ago since the yak rescued them, but I forgot to fix that for chapter three. That has now been amended. I do apologize for any confusion this may cause.

You'll see in chapter 15 why this was a bit of a blunder on my part.