_content: fix directory listings
_content: fix directory listings

The Bytes header and the actual sizes were in different columns.
Also make sure every row has three columns, just in case it matters in the future.

Change-Id: Ifbd56d7426b1e610050ae641e09ac7804ab7070b
Reviewed-on: https://go-review.googlesource.com/c/website/+/362014
Trust: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>
Reviewed-by: Jamal Carvalho <e0195770807aa8c82b0b128d9c0423b5ad035172@golang.org>

golang/website,golang/website,golang/website,golang/website,golang/website,golang/website,golang/website