Add prototype to descriptions

snippets/lowercaseKeys.md

@@ -6,7 +6,7 @@ tags: object,intermediate
 Creates a new object from the specified object, where all the keys are in lowercase.
 
 - 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()`.
+- Convert each key in the original object to lowercase, using `String.prototype.toLowerCase()`.
 
 ```js
 const lowercaseKeys = obj =>