Replace cond with if for shorter, clearer code.

prime.clj/src/prime/clj.clj

@@ -4,9 +4,9 @@
 (require '[clojure.math.numeric-tower :as math])
 
 (defn prime? [x]
-  (cond
+  (if
     (integer? (math/sqrt x)) false
-    :else (every?
+    (every?
        (fn [y] (not= (mod x y) 0))
        (range 2 (math/ceil (math/sqrt x))))))