Fix wrong whitespaces.

This change replaced some tabs with spaces introduced in
change I8b3765713599e34f1411f9bbc7f575ec7c2384e0.

Change-Id: Ia5c23b38c9fbbb46f150e527347b61c64c8d9e87
Signed-off-by: Yuxuan 'fishy' Wang <fishywang@google.com>

org.eclipse.jgit/src/org/eclipse/jgit/gitrepo/RepoCommand.java

@@ -139,7 +139,7 @@ public class RepoCommand extends GitCommand<RevCommit> {
 		 * @param ref
 		 *            The ref (branch/tag/etc.) to read
 		 * @return the sha1 of the remote repository, or null if the ref does
-		 *		   not exist.
+		 *         not exist.
 		 * @throws GitAPIException
 		 */
 		@Nullable