Focus the DOM element after copy

It's annoying that after clicking the <kbd>Copy</kbd> button the flash element remains focused. Then, if you press browser keyboard shortcuts (e.g. <kbd>ALT</kbd> + <kbd>1</kbd> will not switch on the first tab), they will not work.

Sure, we can do:
```js
client.on("complete", function () {
   this.focus();
});
```
But, after my change this is not required. The dom element is focused on `complete`. :smiley: