Incorrect redirects for index

[pancakereport]

I found that the redirects aren't working for index files.

Example with the relevant line
content/01-python_v_stata/index.html -> https://www.econ148.org/textbook/content/python-v-stata/index/

https://www.econ148.org/textbook/content/python-v-stata/index/ is a 404; it should be https://www.econ148.org/textbook/content/python-v-stata/

[pancakereport]

I noticed #3 has mentions of the index file, but I haven't looked closely to see exactly what's going on there. @afeld does your PR fix this?

[afeld]

Yep! 1dc99c1