Hi,
I ran into problem where my builds failed when using newer version of ClojureScript because it clashes with rrb-vector version 0.0.11. More about this problem here: brandonbloom/fipp#42
Dependecy goes like this Ultra -> puget -> fipp -> rrb-vector
Here is the open issue to fix it in cljs-build emezeske/lein-cljsbuild#469
As such I cannot use Ultra. You could override the rrb-vector dependency with this version [quantum/org.clojure.core.rrb-vector "0.0.12"] to make it usable again.