Update space age test to cast to float before rounding.

I'm new to clojure, so when I started out I usually create a new clojure file with tests that just return nil or the input. The input here is a int, so I gave an int back. For at least an hour I was chasing my tail thinking the tests were broken when in reality they were just expecting a float in this function.

This PR just ensures the tests cast the output as a float so other new users don't chaser their tail like I had.

~~~ clojure
user=> (Math/round 10)

IllegalArgumentException No matching method found: round  clojure.lang.Reflector.invokeMatchingMethod (Reflector.java:80)
~~~