I'm honestly not sure Ultra supports Lein 2.8.3. So use that at your own risk.
As of Ultra 0.4.0, Clojure 1.7.x is required due to reader conditional usage in Ultra's dependencies. Ultra 0.3.4 is the last version supporting Clojure 1.6.x. Ultra 0.4.1+ will intelligently fall back to Ultra 0.3.4 if it detects a Clojure version that is below 1.7.0.
Leiningen version 2.5.2+
JDK 8
Note that versions of Ultra prior to 0.5.0 will not play nicely with Clojure 1.9.