Update articles/upgrading/index.adoc

Co-authored-by: caalador <[email protected]>

Author: tepi

articles/upgrading/index.adoc

@@ -173,7 +173,7 @@ Vaadin Quarkus extension is changed to build production package by default. No n
 
 To allow project to keep build configuration unchanged, Vaadin Quarkus extension has `vaadin.build.enabled` property to change the default behavior. Disable Vaadin plugin by adding `vaadin.build.enabled=false` in `application.properties` file to keep using profile based configuration.
 
-== Changes In Theming System
+== Changes in Theming System
 
 Vaadin 25 simplifies the theme/styling system to bring it closer to normal/native web development, and minimizes Vaadin-specific peculiarities, while keeping migration from earlier versions as painless as possible.