chore: release userscript 2.13.0

[github-actions[bot]]

:robot: I have created a release

2.13.0 (2023-07-09)

Features

• support conversation timestamp in markdown export (38f4a97), closes #155

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[github-actions[bot]]

:robot: Release is at https://github.com/pionxzh/chatgpt-exporter/releases/tag/userscript-v2.13.0 :sunflower: