Fix the JDK version documented to build the source code.

Closes: spring-projects#2610
Original pull request: spring-projects#2611.

Author: lanicc

README.adoc

@@ -152,7 +152,7 @@ https://github.com/spring-projects/spring-data-jpa/issues[issue tracker] to see
 == Building from Source
 
 You don’t need to build from source to use Spring Data (binaries in https://repo.spring.io[repo.spring.io]), but if you want to try out the latest and greatest, Spring Data can be easily built with the https://github.com/takari/maven-wrapper[maven wrapper].
-You also need JDK 1.8.
+You also need JDK 17 or above.
 
 [source,bash]
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