Enable line buffering on list URLs FD

s3-bucket-list

@@ -36,7 +36,7 @@ while i < len(sys.argv):
 	elif arg == '--with-list-urls':
 		withListUrls = True
 		try:
-			listUrlsFD = os.fdopen(3, 'w')
+			listUrlsFD = os.fdopen(3, 'w', buffering = 1)
 		except OSError:
 			print('Error: FD 3 not open', file = sys.stderr)
 			sys.exit(1)