Swap `strings` and `modules` sections

Hi!

Thank you so much for the wonderful work! I am enjoying learning rust via rustlings. The best learning experience I had.

In the rust book there are firstly modules and then strings. I see that in the rustling repo the order is reversed.

Is it intentional? Do you mind if I make a PR that swaps them? I think that it is nicer to learn when you don't leap between sections.

https://github.com/rust-lang/rustlings/blob/9a743f80c57cc6bf27819589a8ddb5a5579ab1a4/info.toml#L461-L476

#1938