Fix image_names cpython formatting error

[myselfhimself]

>>> gmic.run("sp apples sp earth print") # No names given
[gmic]-2./ Print images [0,1] = 'apples, earth'.
[0] = 'apples':
  size = (640,400,1,3) [3000 Kio of floats].
  data = (20,22,20,20,20,22,22,22,22,22,22,20,(...),1,1,1,1,1,1,1,1,1,1,1,1).
  min = 1, max = 250, mean = 58.5602, std = 59.8916, coords_min = (317,306,0,1), coords_max = (430,135,0,0).
[1] = 'earth':
  size = (500,500,1,3) [2929 Kio of floats].
  data = (0,0,0,0,0,0,0,0,0,0,0,0,(...),0,0,0,0,0,0,0,0,0,0,0,0).
  min = 0, max = 251, mean = 88.101, std = 69.4635, coords_min = (0,0,0,0), coords_max = (302,262,0,1).
>>> gmic.run("sp apples sp earth print", image_names=["salut", "yo"])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
SystemError: More keyword list entries (4) than format specifiers (3)