isort: fix import order to make travis pass (#490)

pwndbg/heap/ptmalloc.py

@@ -5,7 +5,8 @@ from __future__ import division
 from __future__ import print_function
 from __future__ import unicode_literals
 
-from collections import OrderedDict, namedtuple
+from collections import OrderedDict
+from collections import namedtuple
 
 import gdb