docs: fix simple typo, shat -> that (cookiecutter#1749)

There is a small typo in docs/conf.py.

Should read `that` rather than `shat`.

docs/conf.py

@@ -327,7 +327,7 @@
 # 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 = []