+1 issue:
The 3rd 'go test' should be working like this:
$ go test
go: finding rsc.io/quote v1.5.2
go: downloading rsc.io/quote v1.5.2
go: extracting rsc.io/quote v1.5.2
go: finding rsc.io/sampler v1.3.0
go: finding golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c
go: downloading rsc.io/sampler v1.3.0
go: extracting rsc.io/sampler v1.3.0
go: downloading golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c
go: extracting golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c
PASS
ok example.com/hello 0.023s

but instead it doesn't:
$ go test
hello.go:2:8: no required module provides package rsc.io/quote; to add it:
go get rsc.io/quote
$

Two objections here:

1. It is explicitly stated in the first sentence that this content piece is directed at Go versions 1.11 and 1.12 and
2. this is a blog post and not part of the official documentation. So IMO it holds some historic value and should not be updated, although stating that this is outdated and linking to a more recent post or the official documentation would be sensible.

Here are some pieces of up-to-date documentation Tutorial: Create a Go module and How to Write Go Code.

google search results for 'go modules' , 'go module', 'go module intro', 'go module introduction' all point to this blog post.
A note at the beginning and a link to the intended page should be fine.