Go: dl: add go1.5.4, go1.6.4 and go1.7.6

[perillo]

The golang.org/dl module for some reasons does not include go1.5.x, go1.6.x and go1.7.x.
I tested on my PC and they can be installed correctly. Is there a reason why they should not be included?

Rationale:
I was finding the minimal required Go version to build and test a package, for fun. It worked until go1.8.x. Now I found that it works up to go1.7.x.

[dmitshur]

Issue #18136 was the proposal for implementing this that has more context. It likely wasn't done because golang.org/dl/... (which was originally located in golang.org/x/build/version/...) was created in December of 2016 and Go 1.8 beta was coming out at that time. Go 1.7 was released earlier in 2016. /cc @andybons @josharian @bradfitz Let me know if you're aware of reasons not to do this, but I'm currently not aware of any.

We have downloads available for Go 1.5.x, 1.6.x, and 1.7.x. I think it's reasonable to add commands for them to golang.org/dl. /cc @toothrot @cagedmantis

The latest minor releases of those versions are:

• go1.7.6
• go1.6.4
• go1.5.4

Let's start by adding just those 3 versions. If there's a good reason to add other minor versions and beta/RCs or even older major versions of Go; we can consider doing that afterwards.

The goX.Y.Z command are generated with the golang.org/dl/internal/genv command.

[shihanng]

I would like to try to work on this one if no one is currently working on it.

[dmitshur]

Thanks @shihanng, based on the comments in this issue, it’s all yours.

Keep this in mind:

The goX.Y.Z command are generated with the golang.org/dl/internal/genv command.

(Please see https://golang.org/doc/contribute.html if it’s your first time sending a CL or PR.)

[gopherbot]

Change https://golang.org/cl/221618 mentions this issue: dl: add go.1.5.4, go1.6.4, and go1.7.6