use argparse instead of optparse

refs: #3900

Change-Id: I6a883ef5d481aeac4d92e29249e9368d7b1dcf49
diff --git a/ndn/experiments/experiment.py b/ndn/experiments/experiment.py
index f7284a8..a107905 100644
--- a/ndn/experiments/experiment.py
+++ b/ndn/experiments/experiment.py
@@ -35,7 +35,7 @@
         self.convergenceTime = args["ctime"]
         self.nPings = args["nPings"]
         self.strategy = args["strategy"]
-        self.pctTraffic = float(args["pctTraffic"])
+        self.pctTraffic = args["pctTraffic"]
 
         # Used to restart pings on the recovered node if any
         self.pingedDict = {}