update pkg/errors to v0.9.1

[thaJeztah]

This version plays well with go1.13 and up "wrapped" errors, and makes sure that errors.Unwrap(), errors.Is() and errors.As() are able to get the wrapped error.

[thaJeztah]

Once go < 1.13 is no longer supported by this library, GetExitCode could be rewritten to something like;

// GetExitCode returns the ExitStatus of a process from the error returned by
// exec.Run(). If the exit status is not available an error is returned.
func GetExitCode(err error) (int, error) {
	var exitErr exec.ExitError
	if errors.As(err, &exitErr) {
		if procExit, ok := exitErr.Sys().(syscall.WaitStatus); ok {
			return procExit.ExitStatus(), nil
		}
	}
	return 0, errors.Wrap(err, "failed to get exit code")
}

[dnephin]

Thanks!

I think once go1.11 and go1.12 support is dropped I will probably remove the dependency and use %w.

[thaJeztah]

I think once go1.11 and go1.12 support is dropped I will probably remove the dependency and use %w.

Be careful doing so, because if "downstream" users of this package (not sure if that's something in practice) didn't switch to replace errors.Cause() to errors.Is(), they won't get the underlying error