embedded the mutex into the games global (one fewer global)

game.go

@@ -47,9 +47,9 @@ func (g *game) run() {
 		select {
 		case <-g.kill:
 			log.Printf("game %s: received kill signal, dying gracefully", g.id)
-			gameLock.Lock()
-			delete(games, g.id)
-			gameLock.Unlock()
+			games.Lock()
+			delete(games.m, g.id)
+			games.Unlock()
 			return
 		case p := <-g.register:
 			g.players[p] = true