x/website: mode=json&include=all does not include go1.4-bootstrap-20171003.tar.gz

[perillo]

https://golang.org/dl/?mode=json&include=all shows go1.4-bootstrap-20170518.tar.gz and go1.4-bootstrap-20170531.tar.gz but not the latest go1.4-bootstrap-20171003.tar.gz, linked in https://golang.org/doc/install/source.

[mknyszek]

CC @dmitshur via https://dev.golang.org/owners

[perillo]

After building go1.4 I noted that go version reports go1.4-bootstrap-20170531, that is correctly listed on https://golang.org/dl/?mode=json&include=all. So the file name in https://golang.org/doc/install/source is incorrect.