Improve minDate and maxDate parsing

[alexlafroscia]

Currently, it seems like minDate and maxDate both must be Date objects, otherwise things blow up, because getTime is called on whatever is passed in

ember-pikaday/addon/mixins/pikaday.js

Line 146 in 4097041

const _minDate = new Date(minDate.getTime());

ember-pikaday/addon/mixins/pikaday.js

Line 171 in 4097041

const _maxDate = new Date(maxDate.getTime());

I think that, in both cases, the object should first be converted to a Date (or moment object?`) and then the time extracted.

[alexlafroscia]

This seems to be addressed by #188 so I’ll hold off making a fix in favor of allowing that PR to handle it.