Modified syntax highlighted code blocks to tolerate spaces between the backticks and programming language name.

The GitHub [syntax highlighting example](https://help.github.com/articles/github-flavored-markdown/#syntax-highlighting) shows this:
    ```ruby

```ruby
require 'redcarpet'
markdown = Redcarpet.new("Hello World!")
puts markdown.to_html
```

But spaces after the backticks also works:
    ```   ruby

```   ruby
require 'redcarpet'
markdown = Redcarpet.new("Hello World!")
puts markdown.to_html
```