Broken anchor link and out-of-date content on website version

[airandfingers]

Thanks for writing and publishing this!

I've been reading the version at http://book.mixu.net/distsys/ebook.htm, and I've noticed a couple issues that I'm not sure how to fix:

1. The link to Chapter 4 in the index is broken; it points to http://book.mixu.net/distsys/ebook.html#replication, but that's a chapter 1 subheading.
2. Under the "Primary/backup replication" subheading, text with a typo is displayed: "All updated are performed on the primary" (should be "All updates on..") However, neither input/4_replication.md nor the corresponding output file on current master includes this typo, so I'm guessing the latest build wasn't uploaded to the book.mixu.net server or something.