Remove broken links

README.md

@@ -70,9 +70,6 @@ for its small size and Promises/A+ compatibility.
 
 ## Usage
 
-For a more comprehensive API reference that this polyfill supports, refer to
-https://github.github.io/fetch/.
-
 ### Importing
 
 Importing will automatically polyfill `window.fetch` and related APIs:
@@ -193,7 +190,7 @@ fetch('/avatars', {
 
 * Not all Fetch standard options are supported in this polyfill. For instance,
   [`redirect`](#redirect-modes) and
-  [`cache`](https://github.github.io/fetch/#caveats) directives are ignored.
+  `cache` directives are ignored.
 
 * `keepalive` is not supported because it would involve making a synchronous XHR, which is something this project is not willing to do. See [issue #700](https://github.com/github/fetch/issues/700#issuecomment-484188326) for more information.