Fix NameError in worlddump.py

Change-Id: Ie87e5b5ead777c0153ed7fa5d1db5cc1ae444261
diff --git a/tools/worlddump.py b/tools/worlddump.py
index 0f1a6a1..628a69f 100755
--- a/tools/worlddump.py
+++ b/tools/worlddump.py
@@ -47,7 +47,7 @@
     print cmd
     print "-" * len(cmd)
     print
-    subprocess.Popen(cmd, shell=True)
+    Popen(cmd, shell=True)
 
 
 def _header(name):