Fix docs typo (#206)

Author: chris-morgan

docs/rules/prefer-node-append.md

@@ -1,6 +1,6 @@
 # Prefer `append` over `appendChild`
 
-Enforces the use of, for example, `document.body.append(div);` over `document.body.appendChild(div);` for DOM nodes. There are [some advantages of using `.append()`](https://developer.mozilla.org/en-US/docs/Web/API/ParentNode/append, like the ability to append multiple nodes and to append both [`DOMString`](https://developer.mozilla.org/en-US/docs/Web/API/DOMString) and DOM node objects.
+Enforces the use of, for example, `document.body.append(div);` over `document.body.appendChild(div);` for DOM nodes. There are [some advantages of using `.append()`](https://developer.mozilla.org/en-US/docs/Web/API/ParentNode/append), like the ability to append multiple nodes and to append both [`DOMString`](https://developer.mozilla.org/en-US/docs/Web/API/DOMString) and DOM node objects.
 
 This rule is fixable.