Fix possibly outdated note in 1.9.6 (instanceof)

It seems there are no polymorphic functions in this chapter.

Author: vsemozhetbyt

1-js/09-classes/06-instanceof/article.md

@@ -2,7 +2,7 @@
 
 The `instanceof` operator allows to check whether an object belongs to a certain class. It also takes inheritance into account.
 
-Such a check may be necessary in many cases. Here we'll use it for building a *polymorphic* function, the one that treats arguments differently depending on their type.
+Such a check may be necessary in many cases. For example, it can be used for building a *polymorphic* function, the one that treats arguments differently depending on their type.
 
 ## The instanceof operator [#ref-instanceof]