Added the Grails Bom to example

Author: dauer

grails-data-hibernate5/docs/src/docs/asciidoc/gettingStarted/outsideGrails.adoc

@@ -21,7 +21,7 @@ If you wish to use GORM for Hibernate outside a Grails application you should de
 
 [source,groovy,subs="attributes"]
 ----
-implementation platform("org.apache.grails:{version}")
+implementation platform("org.apache.grails:grails-bom:{version}")
 implementation "org.apache.grails.data:grails-data-hibernate5-core"
 runtimeOnly "com.h2database"
 runtimeOnly "org.apache.tomcat:tomcat-jdbc"