--- original-util.py	2014-06-17 12:50:15.000000000 -0700
+++ util.py	2014-06-17 12:51:33.000000000 -0700
@@ -148,6 +148,9 @@
     log.info("copying file %s -> %s", source, destination)
     with zipio.open(source, 'rb') as fp_in:
         if not dry_run:
+            if os.path.exists(destination):
+                os.unlink(destination)
+
             with open(destination, 'wb') as fp_out:
                 data = fp_in.read()
                 fp_out.write(data)