Remove s/unform call in s/Spec explain*

Trying to workaround the following issue, waiting for an actual fix:
  metosin#262

This path prevents throwing the error:

  java.lang.UnsupportedOperationException: nth not supported on this type: PersistentArrayMap
	at clojure.lang.RT.nthFrom(RT.java:992)
	at clojure.lang.RT.nth(RT.java:940)
	at clojure.spec.alpha$or_spec_impl$reify__2112.unform_STAR_(alpha.clj:1101)
	at clojure.spec.alpha$unform.invokeStatic(alpha.clj:178)
	at clojure.spec.alpha$unform.invoke(alpha.clj:173)
	at clojure.spec.alpha$merge_spec_impl$reify__2190$fn__2193.invoke(alpha.clj:1210)
	at clojure.core$map$fn__5935.invoke(core.clj:2772)
	at clojure.lang.LazySeq.sval(LazySeq.java:42)
	at clojure.lang.LazySeq.seq(LazySeq.java:51)
	at clojure.lang.RT.seq(RT.java:535)
	at clojure.core$seq__5467.invokeStatic(core.clj:139)
	at clojure.core$apply.invokeStatic(core.clj:662)
	at clojure.core$apply.invoke(core.clj:662)
	at clojure.spec.alpha$merge_spec_impl$reify__2190.unform_STAR_(alpha.clj:1210)
	at clojure.spec.alpha$unform.invokeStatic(alpha.clj:178)
	at clojure.spec.alpha$unform.invoke(alpha.clj:173)
	at spec_tools.core.Spec.unform_STAR_(core.cljc:439)
    ...

src/spec_tools/core.cljc

@@ -443,7 +443,7 @@
                      (let [conformed (s/conform* this x)
                            [explain? val] (if (s/invalid? conformed)
                                             [(s/invalid? (conform this x)) x]
-                                            [true (s/unform spec conformed)])]
+                                            [true x])]
                        (if explain?
                          (s/explain* (s/specize* spec) path via in val)
                          [{:path path