CLJS-1944: Can't spec generate non-vector collections

We need to not default gen-into as [], otherwise kind will not be used
when in the gen* implementation.

The fix involves simply copying over a missed change when
Clojure 23e3ec3f8 was copied as ClojureScript cd43ec9.

Author: mfikes

src/main/cljs/cljs/spec.cljs

@@ -795,7 +795,7 @@
   ([form pred {gen-into :into
                :keys [kind ::kind-form count max-count min-count distinct gen-max ::kfn ::cpred
                       conform-keys ::conform-all]
-               :or {gen-max 20, gen-into []}
+               :or {gen-max 20}
                :as opts}
     gfn]
    (let [conform-into gen-into

src/test/cljs/cljs/spec_test.cljs

@@ -100,6 +100,9 @@
   (is (= :b (s/conform ::multi :b)))
   (is (= :a (s/conform ::multi :a))))
 
+(deftest test-cljs-1944
+  (is (not-empty (s/exercise (s/coll-of string? :kind set?)))))
+
 ;; Copied from Clojure spec tests
 
 (def even-count? #(even? (count %)))