Fix typo. Thanks to Christian Clauss for the patch (#181).

Author: vsajip

docs/conf.py

@@ -248,7 +248,7 @@
 # The format is a list of tuples containing the path and title.
 #epub_pre_files = []
 
-# HTML files shat should be inserted after the pages created by sphinx.
+# HTML files that should be inserted after the pages created by sphinx.
 # The format is a list of tuples containing the path and title.
 #epub_post_files = []