fix mini typo (#1559)

fix mini typo

Author: lex111

1-js/09-classes/02-class-inheritance/article.md

@@ -7,7 +7,7 @@ So we can create new functionality on top of the existing.
 
 ## The "extends" keyword
 
-Let's say with have class `Animal`:
+Let's say we have class `Animal`:
 
 ```js
 class Animal {