Update link to Jest Expect docs (#3303)

The existing link lands on a 'this page has moved' placeholder that
doesn't redirect to the correct location. This PR replaces it with the
currently working URL.

packages/react-scripts/template/README.md

@@ -1302,7 +1302,7 @@ it('renders welcome message', () => {
 });
 ```
 
-All Jest matchers are [extensively documented here](http://facebook.github.io/jest/docs/expect.html).<br>
+All Jest matchers are [extensively documented here](http://facebook.github.io/jest/docs/en/expect.html).<br>
 Nevertheless you can use a third-party assertion library like [Chai](http://chaijs.com/) if you want to, as described below.
 
 Additionally, you might find [jest-enzyme](https://github.com/blainekasten/enzyme-matchers) helpful to simplify your tests with readable matchers. The above `contains` code can be written simpler with jest-enzyme.