Use matplotlib to save images

The old one breaks for the new scipy version; replaces image saving with matplotlib.

bob/learn/pytorch/trainers/tflog.py

 # Code referenced from https://gist.github.com/gyglim/1f8dfb1b5c82627ae3efcfbbadb9f514
 import tensorflow as tf
 import numpy as np
-import scipy.misc 
+import matplotlib.pyplot as plt
 try:
     from StringIO import StringIO  # Python 2.7
 except ImportError:
@@ -29,7 +29,7 @@ class Logger(object):
                 s = StringIO()
             except:
                 s = BytesIO()
-            scipy.misc.toimage(img).save(s, format="png")
+            plt.imsave(s, img, format='png')
 
             # Create an Image object
             img_sum = tf.Summary.Image(encoded_image_string=s.getvalue(),