Polish

See gh-20704

Author: snicoll

spring-boot-project/spring-boot-docs/src/docs/asciidoc/spring-boot-features.adoc

@@ -1379,7 +1379,7 @@ These are:
 
 The default unit is milliseconds and can be overridden using `@DurationUnit` as illustrated in the sample above.
 
-TIP: If you are upgrading from a previous version that is simply using `Long` to express the duration, make sure to define the unit (using `@DurationUnit`) if it isn't milliseconds alongside the switch to `Duration`.
+TIP: If you are upgrading a `Long` property, make sure to define the unit (using `@DurationUnit`) if it isn't milliseconds.
 Doing so gives a transparent upgrade path while supporting a much richer format.