Fix saveUnknown throwing errors when value where falsy

[jonathonlui]

When a model has saveUnknown=true and trying to save the model with an unknown attribute with 0 or false values was causing Attribute.setTypeFromRawValue to throw a SchemaError.

I remove the value check from setTypeFromRawValue, which I assume was unnecessarily copied from setType. This allows 0 and false to be correctly converted to dynamo types.

Attributes with the other falsy values like are null, undefined, or 'NaN' are now excluded because it was causing new Attribute to throw TypeError at https://github.com/automategreen/dynamoose/blob/35deac2aaaa418f01b37d9bf8427626a22d142d7/lib/Attribute.js#L12

Also fix the NewModel name test to include missing suffix.

[fishcharlie]

LGTM

[fishcharlie]

Going to keep this open for a bit, just to make sure no one has any other thoughts, and to time this with the release of Dynamoose 0.9. We'll for sure try to get this into version 0.9.

And thank you so much for this!