change "brackets" to "parentheses"

1-js/06-advanced-functions/03-closure/4-closure-sum/solution.md

@@ -1,4 +1,4 @@
-For the second brackets to work, the first ones must return a function.
+For the second parentheses to work, the first ones must return a function.
 
 Like this:
 

1-js/06-advanced-functions/03-closure/4-closure-sum/task.md

@@ -6,7 +6,7 @@ importance: 4
 
 Write function `sum` that works like this: `sum(a)(b) = a+b`.
 
-Yes, exactly this way, via double brackets (not a mistype).
+Yes, exactly this way, using double parentheses (not a mistype).
 
 For instance: