Usage of date.js causes errors

[saslanis]

If you use the date.js library export does not work because date.js parse method returns null while Date.parse returns NaN on wrong dates.

So just change line 345
from

return !/.*%/.test(v) && !isNaN(Date.parse(v));

to

return !/.*%/.test(v) && !(Date.parse(v) == null);

thanks for the tool