Updates golang/go#20672
Change-Id: I88a1d8693ef9d1e4758719603ce1f3c3f6b920bc
Reviewed-on: https://go-review.googlesource.com/79936
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
<p>
To build a bootstrap tool chain from source, use
either the git branch <code>release-branch.go1.4</code> or
-<a href="https://storage.googleapis.com/golang/go1.4-bootstrap-20171003.tar.gz">go1.4-bootstrap-20171003.tar.gz</a>,
+<a href="https://dl.google.com/go/go1.4-bootstrap-20171003.tar.gz">go1.4-bootstrap-20171003.tar.gz</a>,
which contains the Go 1.4 source code plus accumulated fixes
to keep the tools running on newer operating systems.
(Go 1.4 was the last distribution in which the tool chain was written in C.)