Fix internal links

Upgrading-to-Spring-Framework-5.x.md

@@ -1,4 +1,4 @@
-_This page provides guidance on upgrading to Spring Framework [5.0](#Upgrading-to-Version-5.0), [5.1](#Upgrading-to-Version-5.1), and [5.2](#Upgrading-to-Version-5.2). See also the [[Spring-Framework-5-FAQ]] and [[What's New in Spring Framework 5.x]]._
+_This page provides guidance on upgrading to Spring Framework [5.0](#upgrading-to-version-50), [5.1](#upgrading-to-version-51), and [5.2](#upgrading-to-version-52). See also the [[Spring-Framework-5-FAQ]] and [[What's New in Spring Framework 5.x]]._
 
 Currently active branches: Spring Framework 4.3.x and Spring Framework 5.1, with Spring Framework 5.0.x phased out in favor of 5.1 in the second half of 2019. Please upgrade to the latest 5.1.x or 4.3.x release at your earliest convenience!