Avoid confusing prototype methods for static methods

Correct: `Array.from()` (it’s a static method)
Incorrect: `Array.join()` (doesn’t exist; it’s a prototype method)

This patch uses the common `#` syntax to denote `.prototype.`.

snippets/symmetricDifference.md

@@ -2,7 +2,7 @@
 
 Returns the symmetric difference between two arrays, without filtering out duplicate values.
 
-Create a `Set` from each array, then use `Array.filter()` on each of them to only keep values not contained in the other.
+Create a `Set` from each array, then use `Array.prototype.filter()` on each of them to only keep values not contained in the other.
 
 ```js
 const symmetricDifference = (a, b) => {