fix: a bug in secondary constructors (#5331)

Author: danil-pavlov

docs/topics/classes.md

@@ -354,7 +354,7 @@ class Person(val name: String, var age: Int) {
     // Secondary constructor that takes age as a
     // String and converts it to an Int
     constructor(name: String, age: String) : this(name, age.toIntOrNull() ?: 0) {
-        println("$name created with converted age: $age")
+        println("$name created with converted age: ${this.age}")
     }
 }