Fix err in syntax (#1621)

Fix err in syntax

Author: lex111

1-js/09-classes/03-static-properties-methods/article.md

@@ -20,7 +20,7 @@ User.staticMethod(); // true
 That actually does the same as assigning it as a property directly:
 
 ```js run
-class User() { }
+class User { }
 
 User.staticMethod = function() {
   alert(this === User);