Add isPowerOfTwo snippet

snippets/isPowerOfTwo.md

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+---
+title: isPowerOfTwo
+tags: math,beginner
+---
+
+Returns `true` if the given number is a power of `2`, `false` otherwise.
+
+Use the bitwise binary AND operator (`&`) to determine if `n is a power of `2. 
+Additionally, check that `n` is not falsy.
+
+```js
+const isPowerOfTwo = n => !!n && ((n & (n - 1)) == 0);
+```
+
+```js
+isPowerOfTwo(0); // false
+isPowerOfTwo(1); // true
+isPowerOfTwo(8); // true
+```