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/reverseString.md

@@ -2,8 +2,8 @@
 
 Reverses a string.
 
-Use the spread operator (`...`) and `Array.reverse()` to reverse the order of the characters in the string.
-Combine characters to get a string using `String.join('')`.
+Use the spread operator (`...`) and `Array.prototype.reverse()` to reverse the order of the characters in the string.
+Combine characters to get a string using `String.prototype.join('')`.
 
 ```js
 const reverseString = str => [...str].reverse().join('');