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/mask.md

@@ -2,7 +2,7 @@
 
 Replaces all but the last `num` of characters with the specified mask character.
 
-Use `String.slice()` to grab the portion of the characters that will remain unmasked and use `String.padStart()` to fill the beginning of the string with the mask character up to the original length.
+Use `String.prototype.slice()` to grab the portion of the characters that will remain unmasked and use `String.padStart()` to fill the beginning of the string with the mask character up to the original length.
 Omit the second argument, `num`, to keep a default of `4` characters unmasked. If `num` is negative, the unmasked characters will be at the start of the string.
 Omit the third argument, `mask`, to use a default character of `'*'` for the mask.