Auto merge of #42936 - steveklabnik:update-mdbook, r=alexcrichton

update crate dependencies

I wanted to update mdbook's version. This ended up updating a bunch of other stuff too.

I am not sure if updating this much stuff is considered a Good Idea or not; happy to figure out how to make it smaller if someone can help me figure out how to use x.py to do it.

Author: bors