I’ve just got that same error that you mention for bionic. However, I don’t think that’s the reason, but that maybe there’s been a change on the permissions of the page.
In this PR Travis run r-raster-vector-geospatial#325 from a month ago it worked fine, however in a new one from today it shows the 403 forbidden error you mentioned. And for what I’ve found in the forum it may be a temporary problem (though I don’t know what’s the best way to report it).