message: Fix typo in Es6ClassMocks.md
diff: @@ -214,7 +214,7 @@ class, but does not provide a way to spy on calls.
  For the contrived example, the mock might look like this:
  ```javascript
  -// __mocks/sound-player.js
  +// __mocks__/sound-player.js
  export default class SoundPlayer {
  constructor() {
  console.log('Mock SoundPlayer: constructor was called');
  