Fix the unstable book to account for ok-wrapping

Author: scottmcm

src/doc/unstable-book/src/language-features/catch-expr.md

@@ -15,16 +15,16 @@ expression creates a new scope one can use the `?` operator in.
 use std::num::ParseIntError;
 
 let result: Result<i32, ParseIntError> = do catch {
-    Ok("1".parse::<i32>()?
+    "1".parse::<i32>()?
         + "2".parse::<i32>()?
-        + "3".parse::<i32>()?)
+        + "3".parse::<i32>()?
 };
 assert_eq!(result, Ok(6));
 
 let result: Result<i32, ParseIntError> = do catch {
-    Ok("1".parse::<i32>()?
+    "1".parse::<i32>()?
         + "foo".parse::<i32>()?
-        + "3".parse::<i32>()?)
+        + "3".parse::<i32>()?
 };
 assert!(result.is_err());
 ```