Fixed typo in mkdocs.yml

Author: JakeGinnivan

mkdocs.yml

@@ -7,7 +7,7 @@ pages:
 - Changelog: ChangeLog.md
 - Configuration: Configuration.md
 - Getting Started: GettingStarted.md
-- UI Items: UIItemd.md
+- UI Items: UIItems.md
 - Windows: Windows.md
 - FAQ: FAQ.md
 - Screen Objects: