Use build_nested_query, of course

Not quite sure why I assumed build_query would work. I guess
because the tests passed and the tests failed when I used
build_nested query. The issue then however was a bug in rack
(see https://github.com/rack/rack/issues/557), for which this
commit provides a quick fix.
Bump version to 1.3.10

This should be compatible with 1.3.8, this time for real.