pkg/cmd/grafana-server/server.go: Check sendSystemdNotification return value.

See,
$ gometalinter --vendor --deadline 10m --disable-all --enable=errcheck ./...
server.go:165:25:warning: error return value not checked (sendSystemdNotification("READY=1")) (errcheck)

pkg/cmd/grafana-server/server.go

@@ -162,7 +162,11 @@ func (g *GrafanaServerImpl) Run() error {
 		})
 	}
 
-	sendSystemdNotification("READY=1")
+	err = sendSystemdNotification("READY=1")
+	if err != nil {
+		return fmt.Errorf("Could not send systemd notification: %v", err)
+	}
+
 	return g.childRoutines.Wait()
 }