Fix grammatical typo in content-style-guide.md

`the this` -> `this`

contributing/content-style-guide.md

@@ -4,7 +4,7 @@ Welcome to the content style guide for [GitHub Docs](https://docs.github.com/).
 
 These guidelines are specific to GitHub’s documentation. For general style questions or guidance on topics not covered here, see the [GitHub Brand Guide](https://brand.github.com/content/) first, then the [Microsoft Style Guide](https://docs.microsoft.com/style-guide/welcome/). For markup specific to source content on docs.github.com, see our [markup reference guide](content-markup-reference.md).
 
-Use table of contents icon <img src="../assets/images/table-of-contents.png" width="25" height="25" /> on the top left corner of the this document to get to a specific section of this guide quickly.
+Use table of contents icon <img src="../assets/images/table-of-contents.png" width="25" height="25" /> on the top left corner of this document to get to a specific section of this guide quickly.
 
 ## The GitHub Docs approach to style