fix string test

Author: wuxianrong

src/storage/src/redis_strings.cc

@@ -101,7 +101,7 @@ Status Redis::Append(const Slice& key, const Slice& value, int32_t* ret, int64_t
     *ret = static_cast<int32_t>(value.size());
     out_new_value = value.ToString();
     StringsValue strings_value(value);
-    return db_->Put(default_write_options_, key, strings_value.Encode());
+    return db_->Put(default_write_options_, base_key.Encode(), strings_value.Encode()); 
   }
   return s;
 }