MARKDOWN_EXTENSION_CONFIGS is not marked as translatable in default conf.py

[yaram]

Environment

Python Version: Python 3.8.0

Nikola Version: Nikola v8.2.0

Operating System: Windows 10 Build 19043

Description:

The MARKDOWN_EXTENSION_CONFIGS configuration variable is translatable, but is not noted as such in the default conf.py

I plan to submit a pull request modifying conf.py.in to fix this small problem right after submitting this issue.

I wasn't quite sure what issue category to choose, but decided on a bug report, please forgive me if this is the wrong category for this issue.

[Kwpolska]

Just a friendly reminder — I think you forgot to send the PR?