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/filterNonUnique.md

@@ -2,7 +2,7 @@
 
 Filters out the non-unique values in an array.
 
-Use `Array.filter()` for an array containing only the unique values.
+Use `Array.prototype.filter()` for an array containing only the unique values.
 
 ```js
 const filterNonUnique = arr => arr.filter(i => arr.indexOf(i) === arr.lastIndexOf(i));