Fix documentation of BeforeConvertCallback.

Closes #1673

Author: schauder

spring-data-relational/src/main/java/org/springframework/data/relational/core/mapping/event/BeforeConvertCallback.java

@@ -19,7 +19,7 @@
 
 /**
  * An {@link EntityCallback} that gets invoked before the aggregate is converted into a database change. The decision if
- * the change will be an insert or update is made after this callback gets called.
+ * the change will be an insert or update is made before this callback gets called.
  * <p>
  * This is the correct callback if you want to create Id values for new aggregates.
  * <p>