[ci skip]Fix the sample code about Null Relation

Fix the sample code to include 5, as it was incorrectly excluding it despite saying "at least 5."

Author: willnet

guides/source/active_record_querying.md

@@ -1296,7 +1296,7 @@ class Book
   # Returns reviews if there are at least 5,
   # else consider this as non-reviewed book
   def highlighted_reviews
-    if reviews.count > 5
+    if reviews.count >= 5
       reviews
     else
       Review.none # Does not meet minimum threshold yet