Fix issue causing page to jump when focusing element

When scroll to the top of the page, if the date picker is open and rendered partially below the viewport, the browser will jump when closing the date picker. This is easily reproducible in Chrome.

This happens because there is a focus listener on the element that reacts synchronously to the focus event and causes the erratic behavior. I didn't look into exactly why the behavior was what it was.

This is a quick fix. This doesn't happen on the normal version of `pickadate.js` because the input is set to `readOnly` and the focus is handled differently. I looked at upgrading to the latest `pickadate.js` and getting rid of our fork, but there are a number of differences and the behaviors that we added are still not supported.