pkg/cmd/grafana-server/main.go: remove os.Kill as it cannot be trapped

See,
$ gometalinter --vendor --deadline 10m --disable-all --enable=megacheck ./...
pkg/cmd/grafana-server/main.go:103:42:warning: os.Kill cannot be trapped (did you mean syscall.SIGTERM?) (SA1016) (megacheck)

pkg/cmd/grafana-server/main.go

@@ -100,7 +100,7 @@ func listenToSystemSignals(server *GrafanaServerImpl) {
 	sighupChan := make(chan os.Signal, 1)
 
 	signal.Notify(sighupChan, syscall.SIGHUP)
-	signal.Notify(signalChan, os.Interrupt, os.Kill, syscall.SIGTERM)
+	signal.Notify(signalChan, os.Interrupt, syscall.SIGTERM)
 
 	for {
 		select {