Event date is converted to a string by Netlify CMS

Not sure why this is happening -- need to investigate.

More details in the [failed deploy](https://app.netlify.com/sites/the-sunview/deploys/5ad653e6c965923b1cf5aaf1).

Fixed in https://github.com/luncheonette/the-sunview/commit/3fd8e311f61d46ac9eb01ea7e1bc6a465a074ad3