completion: add options --single-branch and --branch to "git clone"

Signed-off-by: NRalf Thielow <ralf.thielow@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

contrib/completion/git-completion.bash

@@ -989,6 +989,8 @@ _git_clone ()
 			--upload-pack
 			--template=
 			--depth
+			--single-branch
+			--branch
 			"
 		return
 		;;