Swap `strings` and `modules` sections

[gzaripov]

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.

rustlings/info.toml

Lines 461 to 476 in 9a743f8

	[[exercises]]
	name = "strings4"
	path = "exercises/strings/strings4.rs"
	mode = "compile"
	hint = "No hints this time ;)"
	# MODULES
	[[exercises]]
	name = "modules1"
	path = "exercises/modules/modules1.rs"
	mode = "compile"
	hint = """
	Everything is private in Rust by default-- but there's a keyword we can use
	to make something public! The compiler error should point to the thing that
	needs to be public."""

#1938

[mo8it]

Closing the PR because of merge conflicts. I will take care of this issue in version 7 (no due date) because it is a breaking change.