Remove void return type for propertyDiff()

[rak3n]

for issue #186

• Add undefined check on onePropertyDiff return value, so as to return empty array from propertyDiff.

[rak3n]

Hey @maritz, many thanks for reviewing, have added test and dropped void from return type. This will modify the way propertyDiff is used in older code to handle no differences in property for a key, so I think it will be a major bump.

[maritz]

This will modify the way propertyDiff is used in older code to handle no differences in property for a key, so I think it will be a major bump.

Yeah, I was thinking so as well. I'm kind of hesitant to just publish a v3 only for this rather minimal change. But on the other hand I can't really promise when other bigger changes are coming.

I guess I'll add this and some dependency updates into a v3 soon and not hold it up for other stuff.