* change instanceof to isDate
* use both methods to check for valid Date
* add test for PR 2862
* use only isDate(date) in place of instanceof Date
* Extend compatibility of `isDate` use back to Node 8
* Clean up test
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Co-authored-by: Charmander <~@charmander.me>
Reviewed-by: Charmander <~@charmander.me>