Add missing @since tag for BatchRefUpdate#getRefDatabase

Change-Id: I5d37cbbd6c338e6e6bb8b95ae13a5ed9b5178a8b
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/lib/BatchRefUpdate.java b/org.eclipse.jgit/src/org/eclipse/jgit/lib/BatchRefUpdate.java
index 21d77f4..d2367cc 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/lib/BatchRefUpdate.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/lib/BatchRefUpdate.java
@@ -525,6 +525,7 @@ public void execute(RevWalk walk, ProgressMonitor monitor,
 	 * Get the ref database associated with this update.
 	 *
 	 * @return the ref database.
+	 * @since 6.6
 	 */
 	protected RefDatabase getRefDatabase() {
 		return refdb;