Fix spelling

PR-URL: #182

Author: fermersky

content/en/2-7-Closure.md

@@ -49,7 +49,7 @@ const res = add(5)(2)(3)(7);
 console.log(res);
 ```
 
-> Abstraction (class sunstitution)
+> Abstraction (class substitution)
 
 ```js
 const COLORS = {

content/ru/2-7-Closure.md

@@ -49,7 +49,7 @@ const res = add(5)(2)(3)(7);
 console.log(res);
 ```
 
-> Abstraction (class sunstitution)
+> Abstraction (class substitution)
 
 ```js
 const COLORS = {