Should throw RangeError if not date string

[iyobo-vivun]

Native Javascript date throws a RangeError when trying to parse a bad date e.g new Date("not-a-date").
timezone-mock throws an AssertionError in this case.

It really should throw a RangeError like native javascript Date object.

[Jimbly]

Exactly which strings cause native JavaScript to throw which errors is very platform-dependent (as well as locale-dependent), some strings will throw an error on Firefox, but not Node, some will throw an error in a Norwegian locale, but not in the UK. It's infeasible for this library to handle all of those in a reasonable way, and probably if code is passing any of those strings to a Date constructor, then that code is potentially faulty.