Fix line numbers

Fixes #69.

strings/strings2.rs

@@ -41,4 +41,4 @@ fn is_a_color_word(attempt: &str) -> bool {
 
 // Yes, it would be really easy to fix this by just changing the value bound to `word` to be a
 // string slice instead of a `String`, wouldn't it?? There is a way to add one character to line
-// 5, though, that will coerce the `String` into a string slice.
+// 6, though, that will coerce the `String` into a string slice.