CLJS-225: fix warning about undeclared Var in cljs.reader

The reason was a typo in read-keyword; the resulting function worked
because cljs.core/keyword's binary variant currently delegates to the
unary variant anyway.

src/cljs/cljs/reader.cljs

@@ -262,7 +262,7 @@ nil if the end of stream has been reached")
             (identical? (aget name (dec (.-length name))) ":")
             (not (== (.indexOf token "::" 1) -1)))
       (reader-error reader "Invalid token: " token)
-      (if ns?
+      (if ns
         (keyword (.substring ns 0 (.indexOf ns "/")) name)
         (keyword token)))))