Updating USER_INPUT_SELECTOR for scripts/export.js

[djdarcy]

As of 2023.10.23 the export function isn't working because OpenAI changed the formatting for the user div class. This is a small edit to USER_INPUT_SELECTOR to bring it up-to-date.

https://github.com/djdarcy/DJChatGPT/commit/1738a42ac966cda1d574db51d8326fc7704a1aa8#diff-07730f255965d05b06fd534bacae2f4821dac223b364e725b8df6c53ad16503a

The scripts/markdown.export.js change isn't wholly necessary (just a personal tweak for my own purposes).

[Arvin2focus]

this patch did not seem to work。