Update isPrime.md

snippets/isPrime.md

@@ -8,7 +8,7 @@ Return `false` if any of them divides the given number, else return `true`, unle
 ```js
 const isPrime = num => {
   const boundary = Math.floor(Math.sqrt(num));
-  for (var i = 2; i * i <= boundary; i++) if (num % i == 0) return false;
+  for (var i = 2; i <= boundary; i++) if (num % i == 0) return false;
   return num >= 2;
 };
 ```