Update regex example (#367)

* prefer LazyLock from rust std library

* fix error in regex example

Author: mjanssen

README.md

@@ -251,13 +251,13 @@ Tests whether the string matches the regex given. `regex` takes
 Examples:
 
 ```rust
-use once_cell::sync::Lazy;
+use std::sync::LazyLock;
 
 static RE_TWO_CHARS: Lazy<Regex> = Lazy::new(|| {
     Regex::new(r"[a-z]{2}$").unwrap()
 });
 
-#[validate(regex(path = *RE_TWO_CHARS)]
+#[validate(regex(path = *RE_TWO_CHARS))]
 ```
 
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