Add an example of doing valueMap restricted to all keys but the specified ones

[krlawrence]

An example along these lines would be useful to add.

gremlin> g.V('3').valueMap().as('vm').unfold().filter(select(keys).is(without('city','desc')))
==>country=[US]
==>code=[AUS]
==>longest=[12250]
==>elev=[542]
==>icao=[KAUS]
==>lon=[-97.6698989868164]
==>type=[airport]
==>region=[US-TX]
==>runways=[2]
==>lat=[30.1944999694824]