Update README.md to fix HTTPResponseError

[thedanfernandez]

In the 'Handling client and server errors', the class HTTPResponseError constructor has to call 'super()' before accessing 'this.response'

Not doing this throws the following exception: "ReferenceError: Must call super constructor in derived class before accessing 'this' or returning from derived constructor"

Fix: This just changes the order so super(...) is first, then this.response...

MDN Reference: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/super#using_super_in_classes

What is the purpose of this pull request?

• Documentation update
• Bug fix
• New feature
• Other, please explain:

What changes did you make? (provide an overview)
README.md

• The PR just moves the line this.response = response; to after the super() function as shown below.

		super(`HTTP Error Response: ${response.status} ${response.statusText}`, ...args);
		this.response = response;

Which issue (if any) does this pull request address?

Is there anything you'd like reviewers to know?
Thanks for all that you do :)