Update reading_progress vendor version number

[liolok]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines.
• Tests for the changes was maked (for bug fixes / features).
  • Muse | Mist have been tested.
  • Pisces | Gemini have been tested.
• Docs in NexT website have been added / updated (for features).

PR Type

What kind of change does this PR introduce?

• Bugfix.
• Feature.
• Code style update (formatting, local variables).
• Refactoring (no functional changes, no api changes).
• Build related changes.
• CI related changes.
• Documentation content changes.
• Other... Please describe:

How to use?

In NexT _config.yml:

-  # Internal version: 1.1
+  # Internal version: 1.2.0
  # See: https://github.com/theme-next/theme-next-reading-progress
  # Example:
-  # reading_progress: //cdn.jsdelivr.net/gh/theme-next/theme-next-reading-progress@1/reading_progress.min.js
+  # reading_progress: //cdn.jsdelivr.net/gh/theme-next/theme-next-reading-progress@1.2.0/reading_progress.min.js
  reading_progress:

Does this PR introduce a breaking change?

• Yes.
• No.

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