Update react-controls-platform-libraries.md

Fix typo

Author: JimDaly

powerapps-docs/developer/component-framework/react-controls-platform-libraries.md

@@ -67,7 +67,7 @@ After you build the control, you can package it inside solutions and use it for
 
 ## Differences from standard components
 
-Thi section describes the differences between a React component and a standard component.
+This section describes the differences between a React component and a standard component.
 
 ### ControlManifest.Input.xml