Fix params for saved card csv downloading

src/metabase/api/card.clj

 (ns metabase.api.card
   (:require [clojure.data :as data]
+            [cheshire.core :as json]
             [compojure.core :refer [GET POST DELETE PUT]]
             [schema.core :as s]
             (metabase.api [common :refer :all]
@@ -273,9 +274,11 @@
   (run-query-for-card card-id parameters))
 
 (defendpoint POST "/:card-id/query/csv"
-  "Run the query associated with a Card, and return its results as CSV."
-  [card-id :as {{:keys [parameters]} :body}]
-  (dataset-api/as-csv (run-query-for-card card-id parameters)))
+  "Run the query associated with a Card, and return its results as CSV. Note that this expects the query as serialized JSON in the 'query' parameters."
+  [card-id query]
+  {query (s/maybe su/JSONString)}
+  (dataset-api/as-csv (run-query-for-card card-id (when query
+                                                    (:parameters (json/parse-string query keyword))))))
 
 (defendpoint GET "/:card-id/json"
   "Fetch the results of a Card as JSON."