Follow #operate method signature change. Fix #112

Since #105, #operate method need 3 arguments.
This commit follows this change.

Signed-off-by: Hiroshi Hatake <hatake@clear-code.com>

Author: cosmo0920

lib/fluent/plugin/out_mongo_replset.rb

@@ -35,9 +35,9 @@ def write(chunk)
 
     private
 
-    def operate(client, records)
+    def operate(database, client, records)
       rescue_connection_failure do
-        super(client, records)
+        super(database, client, records)
       end
     end