Title in front matter overrides theme config

[morrislaptop]

@ulivz @yyx990803 does this cause a double up in the title meta tag.

If I have...

module.exports = {
  title: 'Theme Title',
}

and

---
layout: about
title: About Us
---

I get <title>About Us | About Us</title>

Whereas, if I have:

---
layout: about
---

About Us

I get <title>About Us | Theme Title</title>