server: unbuffered signal channel could cause signal not to be delivered

[odeke-em]

Coming here from auditing

keyrace/server.go

Lines 281 to 283 in dab1b87

	signals := make(chan os.Signal)
	signal.Notify(signals, os.Interrupt)
	signal.Notify(signals, syscall.SIGTERM)

which is a bug as documented in os/signal https://golang.org/pkg/os/signal/#Notify as per:

For Go1.17, my team is going to release a static analyzer that'll be included when you run go test as per golang/go#9399, but for now, please make that channel buffered.

Our internal static analyzer reports this:

$ sigchanyzer ./server.go 
github.com/nat/keyrace/server.go:282:2: misuse of unbuffered os.Signal channel as argument to signal.Notify

/cc @cuonglm