add plaintext url

gemini/benchmark_config

@@ -8,8 +8,9 @@
       "query_url": "/db?queries=",
       "fortune_url": "/fortunes",
       "update_url": "/update?queries=",
+      "plaintext_url": "/plaintext",
       "port": 8080,
       "sort": 0
     }
   }]
-}
+}