internal/fetch: increase max documentation size
internal/fetch: increase max documentation size

Some popular packages have documentation sizes that exceed our
limit. Double the limit to include them and leave room for them to
grow even larger.

Marking the issue fixed, though changes won't appear until we next
reprocess.

Fixes golang/go#40576.

Change-Id: I5cc37a46949e23370de5c2104fee1e323228de10
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/246678
Reviewed-by: Jamal Carvalho <e0195770807aa8c82b0b128d9c0423b5ad035172@golang.org>

golang/pkgsite,golang/pkgsite,golang/pkgsite,golang/pkgsite