Fix typo in configuration docs (mmistakes#2497)

`https://github.io.mmistakes` should be `https://mmistakes.github.io`

Author: tobiasvl

docs/_docs/05-configuration.md

@@ -157,7 +157,7 @@ _Example:_ `description: "A flexible Jekyll theme for your blog or site with a m
 
 ### Site URL
 
-The base hostname and protocol for your site. If you're hosting with GitHub Pages this will be something like `url: "https://github.io.mmistakes"` or `url: "https://mademistakes.com"` if you have a custom domain name.
+The base hostname and protocol for your site. If you're hosting with GitHub Pages this will be something like `url: "https://mmistakes.github.io"` or `url: "https://mademistakes.com"` if you have a custom domain name.
 
 GitHub Pages now [forces `https://` for new sites](https://help.github.com/articles/securing-your-github-pages-site-with-https/) so be mindful of that when setting your URL to avoid mixed-content warnings.