fix: replace DefaultPrng with std.crypto.random

See https://lobste.rs/s/jih1sc/zig_cookbook_collection_simple_zig#c_8wncpt

book-src/06-01-rand.md

@@ -1,11 +1,9 @@
 ## Generate random numbers
 
-Generates random numbers with help of random-number generator [`std.rand.Random`].
-
-Currently the default pseudorandom number generator(PRNG) used in Zig is [Xoshiro256++](https://prng.di.unimi.it/).
+Generates random numbers with help of a thread-local, cryptographically secure pseudo random number generator [`std.crypto.random`].
 
 ```zig
 {{#include ../src/06-01.zig }}
 ```
 
-[`std.rand.random`]: https://ziglang.org/documentation/0.11.0/std/#A;std:rand.Random
+[`std.crypto.random`]: https://ziglang.org/documentation/0.11.0/std/#A;std:crypto.random

src/06-01.zig

@@ -2,8 +2,7 @@ const std = @import("std");
 const print = std.debug.print;
 
 pub fn main() !void {
-    var prng = std.rand.DefaultPrng.init(@intCast(std.time.timestamp()));
-    const rand = prng.random();
+    const rand = std.crypto.random;
 
     print("Random u8: {}\n", .{rand.int(u8)});
     print("Random u8 less than 10: {}\n", .{rand.uintLessThan(u8, 10)});