Update 05-configuration.md

- fix dead Twitter Dev docs url
- slight clarification re: Player Card approval
- fix Jekyll docs url

docs/_docs/05-configuration.md

@@ -677,7 +677,7 @@ twitter:
 
 And if I assign `@mmistakes` as an author account it will appear in the Twitter Card along with `@mmistakes-theme`, attributed as a creator of the page being shared.
 
-**Note**: You need to [apply for Twitter Cards](https://dev.twitter.com/docs/cards) and validate they're working on your site before they will begin showing up.
+**Note**: You need to validate cards are working and have Twitter [approve Player Cards](https://developer.twitter.com/en/docs/tweets/optimize-with-cards/overview/player-card) before they will begin showing up.
 {: .notice--warning}
 
 ##### Facebook Open Graph
@@ -855,7 +855,7 @@ Again nothing out of the ordinary here as the theme adheres to the defaults used
 
 ## Front Matter Defaults
 
-To save yourself time setting [Front Matter Defaults](https://jekyllrb.com/docs/configuration/#front-matter-defaults) for posts, pages, and collections is the way to go. Sure you can assign layouts and toggle settings like **reading time**, **comments**, and **social sharing** in each file, but that's not ideal.
+To save yourself time setting [Front Matter Defaults](https://jekyllrb.com/docs/configuration/front-matter-defaults/) for posts, pages, and collections is the way to go. Sure you can assign layouts and toggle settings like **reading time**, **comments**, and **social sharing** in each file, but that's not ideal.
 
 Using the `default` key in `_config.yml` you could set the layout and enable author profiles, reading time, comments, social sharing, and related posts for all posts --- in one shot.