temp. removed swimmer from gallery

examples/conf.py

@@ -47,7 +47,6 @@ napoleon_use_rtype = False
 # images for the gallery
 nbsphinx_thumbnails = {
     'solarsail/solarsail-simple-version': 'solarsail/solarsail.jpeg',
-    'swimmer/swimmer': 'swimmer/swimmer.jpeg',
     'substrate/depletion': 'substrate/depletion.png',
     'bacteria/bacteria': 'bacteria/maintenance.png',
     'bistable/bistable': 'bistable/thumbnail.png',