github: fix unbuffered channel passed to signal.Notify

The docs at os/signal.Notify warn about this signal delivery loss bug at
https://golang.org/pkg/os/signal/#Notify, which says:

    Package signal will not block sending to c: the caller must ensure
    that c has sufficient buffer space to keep up with the expected signal
    rate. For a channel used for notification of just one signal value,
    a buffer of size 1 is sufficient.

Caught by a static analysis tool from Orijtech, Inc. called "sigchanyzer"

Fixes https://github.com/github/hub/issues/2616

fix: Update checkout and cache to v2

Fix parsing boolean flags with explicit values

Fixes #2590

Avoid literal mention of "GitHub CLI" because hub already ranks too high
for those search terms and we don't want it to rank any higher.

Closes #2458

It's just a bad system for this kind of CLI application.

Closes https://github.com/github/hub/issues/2565

Add Void and Gentoo to installation instructions

see https://github.com/conda-forge/hub-feedstock for conda-forge hub package.

Fixes #2552

Ref. d99f308e

Fix typos

add /v2 to the module name to resolve the module path problem

Fixes  #2517

Linting Cleanup

This was put in place for Go < 1.11, which we no longer support in CI.

This reverts commit 75c54101.

remove bmizerany/assert