support newly nrepl

My nREPL is cider 0.8.1.
CIDER 0.8.1 (package: 20141124.2036) (Java 1.7.0_71, Clojure 1.6.0, nREPL 0.2.6) 
In that case, return value of `nrepl-send-string-sync` function is looks like,
```
(dict "err" "..." "id" "9" "session" "b614a748-c33d-49d8-9b99-4dcc678fdcf5" "out" "(ns clj-tms.http                                                                                                             
  (:require [cheshire.core :as json]                                                                                                                                                                            
            [clj-http.client :as http]))" "ns" "user" "value" "nil" "status" ("done")) 
```
Key `:stdout` change to `out` string.
So I fixed it.
How about?