chore: fixed minor typo

exercises/23_conversions/from_into.rs

@@ -25,7 +25,7 @@ impl Default for Person {
 }
 
 // Your task is to complete this implementation in order for the line `let p =
-// Person::from("Mark,20")` to compile Please note that you'll need to parse the
+// Person::from("Mark,20")` to compile. Please note that you'll need to parse the
 // age component into a `usize` with something like `"4".parse::<usize>()`. The
 // outcome of this needs to be handled appropriately.
 //