vmg/redcarpet — pull request #389 by namusyaka (2014-06-11 14:29:49+00:00)
Title: A hyphen and a equal should not be converted to heading

Hello.
I guess a hyphen and a equal should not be converted to heading.
For example, this code will convert to heading.
```ruby
redcarpet = Redcarpet::Markdown.new(Redcarpet::Render::HTML)
redcarpet.render("-") #=> "

\n"
# But, I'd expected "

-

\n"
```
Please review, thanks.