Updated the regex and alertText of the date field to the Dutch date notation.

I've implemented form validation for a couple of Dutch websites and I noticed that the date notation is not the correct standard. The normal ISO 8601 notation is YYYY-MM-DD but the Dutch standard is DD-MM-YYYY.
Updated the alertText of the Date field

Removed a typo
Merge pull request #740 from DennisBruijn/patch-1

Updated the regex and alertText of the date field to the Dutch date nota...