common Dutch language error

It is a common dutch error to use 'als' when it should be 'dan'.
In this case it should be 'dan', see for instance
http://taaladvies.net/taal/advies/vraag/354/ (dutch)
Merge pull request #194 from rubenrorije/master

small dutch language error in StringMaxLengthRule /Csla/Properties/Resources.nl.resx