Update to `go install` and module to v2

[ghthor]

You can create a patch from my fork here. You didn't fork from yudai/gotty so I can't send a PR with the changes.

https://github.com/ghthor/gotty/commit/9aea12400659d78a070bf1f8a1caff59bcf19f01

[sorenisanerd]

I had originally forked from yuday/gotty, but got Github to remove that link. There was too much tooling that assumed that the focus of development was his fork.

I realized that the v2 stuff was a mistake, in part because of the problem you're highlighting. It's just a bad user experience to have to add the /v2/ bit when you're installing and gotty isn't a library. SemVer isn't very important for gotty. Now that 1.4.0 is out, I'm going to try to see if I need to retract any of the v2+ stuff and get this sorted out once and for all.

[sorenisanerd]

I left some comments on the linked commit. :)