Cosmetic change s/Guides/guides/

* s/Guides/guides/

CONTRIBUTING.md

@@ -45,7 +45,7 @@ If you don't see your idea listed, and you think it fits into the goals of this
 * **If your contribution is major,** such as a new guide, start by opening an issue first. That way, other people can weigh in on the discussion before you do any work.
 
 ## Style guide
-If you're writing content, see the [style guide](./docs/styleguide.md) to help your prose match the rest of the Guides.
+If you're writing content, see the [style guide](./docs/styleguide.md) to help your prose match the rest of the guides.
 
 ## Setting up your environment