Pillow online manual is gone - link against stable

doc/conf.py

@@ -243,10 +243,7 @@ intersphinx_mapping['http://scikit-image.org/docs/%s.x' % skimage_version] = \
     None
 
 # Add PIL link
-pil_version = pkg_resources.require('pillow')[0].version
-pil_version = '.'.join(pil_version.split('.')[:2])
-intersphinx_mapping['http://pillow.readthedocs.io/en/%s.x' % pil_version] = \
-    None
+intersphinx_mapping['http://pillow.readthedocs.io/en/stable'] = None
 
 # We want to remove all private (i.e. _. or __.__) members
 # that are not in the list of accepted functions