Update dependency pymdown-extensions to v7.1

[renovate]

This PR contains the following updates:

Package	Update	Change
pymdown-extensions	minor	==7.0 -> ==7.1

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Release Notes

facelessuser/pymdown-extensions

v7.1

Compare Source

7.1

• NEW: SuperFences will now allow number ranges in hl_lines option. (#​878)
• NEW: Emoji extension now requires custom emoji indexes to take an options and md argument. The old non-argument format is deprecated and still accepted, but support for indexes with no arguments will be removed at a future time.
• NEW: Highlight now allows the specifying of a custom line number class when not using Pygments.
• FIX: Better Arithmatex patterns. Fix issue #​888 which caused a hang due to a regular expression typo. Also ensure #!tex $$..$$ and #!tex begin{}...end{} patterns properly don't match if the tail markers are escaped.

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