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/lowercaseKeys.md

@@ -2,7 +2,7 @@
 
 Creates a new object from the specified object, where all the keys are in lowercase.
 
-Use `Object.keys()` and `Array.reduce()` to create a new object from the specified object.
+Use `Object.keys()` and `Array.prototype.reduce()` to create a new object from the specified object.
 Convert each key in the original object to lowercase, using `String.toLowerCase()`.
 
 ```js