`valueMap` step returns properties in random order

`valueMap` step return properties in random order. In most cases it's not important, but
but for example this does not allow using `by` modulators correctly.
In this example I expect to get `name` unfolded, but modulator applied to `location`

gremlin> g = TinkerFactory.createTheCrew().traversal()
==>graphtraversalsource[tinkergraph[vertices:6 edges:14], standard]
gremlin> g.V(1).valueMap("location","name").by().by(__.unfold())
==>[name:[marko],location:san diego]