This querySelector is wrong formated and raises a DOMException

This code line creates a wrongly formated selector for document.querySelector and results into a DOMException

https://github.com/adopted-ember-addons/ember-pikaday/blob/19366ea66e9037fe9410c65369e9bb796a4b5ed6/addon/helpers/pikaday.js#L40

for example day=5 gives
```
'td[data-day="'5'"]:not(.is-outside-current-month) button}'
```
which is wrong in two places the last } is too much and encasing the day placeholder with ' also brakes the selector. The right code line could look like this
```
`td[data-day="${day}"]:not(.is-outside-current-month) button`
```

Start at addon/helpers/pikaday.js line 40 and inspect the selector passed to document.querySelector. Reproduce the day=5 case, then verify that the selector no longer raises a DOMException and targets the intended button.

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