Use ok alias for consistency

Change instance of schema/optional-key to use ok alias instead
for consistency with the rest of the file.

src/clj/puppetlabs/http/client/common.clj

@@ -68,8 +68,7 @@
    :body            Body
    :decompress-body schema/Bool
    :as              BodyType
-   (schema/optional-key
-     :persistent)   schema/Bool})
+   (ok :persistent) schema/Bool})
 
 (def SslContextOptions
   {:ssl-context SSLContext})