install: use stable tag.

[MikeMcQuaid]

Currently we always install onto the latest master. Instead, let's correctly use the latest tag.

See also Homebrew/brew#16891

[vitorgalvao]

Should the “untar anywhere” instructions be updated as well, for parity? Though I can see the argument that the extra complication that could add to the command isn’t worth it in support terms.

[MikeMcQuaid]

Though I can see the argument that the extra complication that could add to the command isn’t worth it in support terms.

Yeh, that's my thinking really. It'll get fixed the first time you run brew update anyway.

[Bo98]

Also fixes #829 I think?

[Bo98]

update.sh technically does refs/tags/${LATEST_GIT_TAG} to avoid any name clash, though not sure if that matters much.

[MikeMcQuaid]

update.sh technically does refs/tags/${LATEST_GIT_TAG} to avoid any name clash, though not sure if that matters much.

@Bo98 yeh, can't see it mattering here but can update if it does!

Thanks all!