Remove confusing ECMAScript 5 reference (fixes nzakas#299)

Author: nzakas

manuscript/04-Objects.md

@@ -363,7 +363,7 @@ The actual value of an object's prototype is stored in an internal-only property
 
 ### Easy Prototype Access with Super References
 
-As previously mentioned, prototypes are very important for JavaScript and a lot of work went into making them easier to use in ECMAScript 6. Another improvement is the introduction of `super` references, which make accessing functionality on an object's prototype easier. For example, to override a method on an object instance such that it also calls the prototype method of the same name, you'd do the following in ECMAScript 5:
+As previously mentioned, prototypes are very important for JavaScript and a lot of work went into making them easier to use in ECMAScript 6. Another improvement is the introduction of `super` references, which make accessing functionality on an object's prototype easier. For example, to override a method on an object instance such that it also calls the prototype method of the same name, you'd do the following:
 
 ```js
 let person = {