Add missing @since to new API

Change-Id: Ie7c3481aba515d9c9b0a152db17b5a9dc74e7ede
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>

org.eclipse.jgit/src/org/eclipse/jgit/revwalk/BitmappedObjectReachabilityChecker.java

@@ -25,6 +25,8 @@ import org.eclipse.jgit.lib.BitmapIndex.BitmapBuilder;
 /**
  * Checks if all objects are reachable from certain starting points using
  * bitmaps.
+ *
+ * @since 5.8
  */
 public class BitmappedObjectReachabilityChecker
 		implements ObjectReachabilityChecker {