[ci skip] remove the timestamp from the doc (to avoid useless commits when the doc did not change)

docs/conf.py

@@ -178,6 +178,8 @@ html_static_path = ['_static']
 # If not '', a 'Last updated on:' timestamp is inserted at every page bottom,
 # using the given strftime format.
 #html_last_updated_fmt = '%b %d, %Y'
+# remove timestamp to avoid too many commits
+html_last_updated_fmt = None
 
 # If true, SmartyPants will be used to convert quotes and dashes to
 # typographically correct entities.