cmd/present: fix indentation in template

No semantic change.
Pointed out by Dmitri Shuralyov on CL 33578.

Change-Id: Ic67f41e8dde8fc9bf624c98307a89bbe1f10e7f7
Reviewed-on: https://go-review.googlesource.com/33659
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
1 file changed