clearer doc with compile_fail

Author: Canop

Cargo.toml

@@ -9,7 +9,7 @@ license = "MIT"
 categories = ["text-processing"]
 repository = "https://github.com/Canop/lazy-regex"
 readme = "README.md"
-rust-version = "1.56"
+rust-version = "1.65"
 
 [dependencies]
 once_cell = "1.7"

src/lib.rs

@@ -58,8 +58,10 @@ let r = regex!(r#"(?x)
 assert_eq!(r.find("This is lazy_regex-2.2!").unwrap().as_str(), "lazy_regex-2.2");
 // (look at the regex_captures! macro to easily extract the groups)
 
-// this line wouldn't compile because the regex is invalid:
-// let r = regex!("(unclosed");
+```
+```compile_fail
+// this line doesn't compile because the regex is invalid:
+let r = regex!("(unclosed");
 
 ```
 Supported regex flags: `i`, `m`, `s`, `x`, `U`.