(CLJS) cljs alts! not non-deterministic

In cljs, clojure.core.async/random-array's shuffle was incorrect, leading it to always return [1 0] for arg n=2. This breaks the promise that alts! is non-deterministic w.r.t. op selection by always trying the second element first. Additionally, the first op is never chosen first for alts! of any size N>1.

Use goog.array.shuffle to do the shuffle instead. (This API is also used by cljs.core/shuffle)

New implementation passes tests and behaves better: