completion: add --interactive option to git svn dcommit

see afd7f1e for more details on git svn dcommit --interactive

Signed-off-by: Frederic Heitzmann <frederic.heitzmann@gmail.com>
Acked-by: Eric Wong <normalperson@yhbt.net>

contrib/completion/git-completion.bash

@@ -2512,7 +2512,7 @@ _git_svn ()
 			__gitcomp "
 				--merge --strategy= --verbose --dry-run
 				--fetch-all --no-rebase --commit-url
-				--revision $cmt_opts $fc_opts
+				--revision --interactive $cmt_opts $fc_opts
 				"
 			;;
 		set-tree,--*)