Fix doc (#4792)

Author: xfumihiro

docs/UsingMatchers.md

@@ -98,7 +98,7 @@ For floating point equality, use `toBeCloseTo` instead of `toEqual`, because you
 ```js
 test('adding floating point numbers', () => {
   const value = 0.1 + 0.2;
-  expect(value).not.toBe(0.3);    // It isn't! Because rounding error
+//expect(value).toBe(0.3);           This won't work because of rounding error
   expect(value).toBeCloseTo(0.3); // This works.
 });
 ```