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/flattenObject.md

@@ -3,7 +3,7 @@
 Flatten an object with the paths for keys.
 
 Use recursion.
-Use `Object.keys(obj)` combined with `Array.reduce()` to convert every leaf node to a flattened path node.
+Use `Object.keys(obj)` combined with `Array.prototype.reduce()` to convert every leaf node to a flattened path node.
 If the value of a key is an object, the function calls itself with the appropriate `prefix` to create the path using `Object.assign()`.
 Otherwise, it adds the appropriate prefixed key-value pair to the accumulator object.
 You should always omit the second argument, `prefix`, unless you want every key to have a prefix.