RUBY-1028: Improve performance of cursor namespace injection

Author: durran

lib/mongo/monitoring/event/command_succeeded.rb

@@ -98,7 +98,7 @@ def self.generate_reply(command_payload, reply_payload)
           if reply_payload
             reply = reply_payload[:reply]
             if cursor = reply[:cursor]
-              reply = reply.merge(cursor: cursor.merge(ns: namespace(command_payload)))
+              cursor.merge!('ns' => namespace(command_payload)) if !cursor.key?('ns')
             end
             reply
           else