Fix set() calls in WeakMap and WeakSet article

Author: Sarratas

article.md

@@ -132,7 +132,7 @@ let visitsCountMap = new Map(); // map: user => visits count
 // increase the visits count
 function countUser(user) {
   let count = visitsCountMap.get(user) || 0;
-  visitsCountMap.set(count + 1);
+  visitsCountMap.set(user, count + 1);
 }
 ```
 
@@ -162,7 +162,7 @@ let visitsCountMap = new WeakMap(); // map: user => visits count
 // increase the visits count
 function countUser(user) {
   let count = visitsCountMap.get(user) || 0;
-  visitsCountMap.set(count + 1);
+  visitsCountMap.set(user, count + 1);
 }
 ```