strip_yaml_front_matter work incorrectly when the file body containts '---'

[kliu]

All the contents after the front-matter and before the last one --- will be deleted when the strip_yaml_front_matter option is true.

For example:

---
layout: post
title: "Test"

---

foo

---
bar

The foo will not appear in the exported html.

This issue also affects the file that contains the markdown fromat table.

[facelessuser]

This is actually a pretty easy fix. The regex is just being too greedy. I will patch this in the next release.

[facelessuser]

This should now be fixed.