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/mapString.md

@@ -2,8 +2,8 @@
 
 Creates a new string with the results of calling a provided function on every character in the calling string.
 
-Use `String.split('')` and `Array.map()` to call the provided function, `fn`, for each character in `str`.
-Use `Array.join('')` to recombine the array of characters into a string.
+Use `String.prototype.split('')` and `Array.prototype.map()` to call the provided function, `fn`, for each character in `str`.
+Use `Array.prototype.join('')` to recombine the array of characters into a string.
 The callback function, `fn`, takes three arguments (the current character, the index of the current character and the string `mapString` was called upon).
 
 ```js