default & 64MB screenshots of GC are the same

[pinko-fowle]

The screenshots in https://github.com/aliyun-node/Node.js-Troubleshooting-Guide/blob/master/0x08_%E5%AE%9E%E8%B7%B5%E7%AF%87_%E7%BB%BC%E5%90%88%E6%80%A7%20GC%20%E9%97%AE%E9%A2%98%E5%92%8C%E4%BC%98%E5%8C%96.md show exactly the same GC performance in the default settings & at 64MB. The article says the performance has increased significantly, but with the same image being used in both, it's hard to see what the improvement really is.