Fix pandoc version detection in Makefile, so markdown-smart is used and double dashes don't get converted to single hyphens in the man page

[t-nil]

…hen or equal to 2

See yt-dlp/yt-dlp#7046

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What is the purpose of your pull request?

• Bug fix

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Description of your pull request and other information

The makefile had a hardcoded major version check of pandoc against 2. In my pandoc 3 installation the check failed and smart-markdown was not used, even though it is available. That caused double dashes to be rendered as single, long dashes.

This PR fixes the version check by numerically comparing the pandoc major version to be greater then or equal to 2.

[dirkf]

Obviously not related to the issue, but this can be done just in POSIX shell, under the assumption that the major version is the digit string at the start of the second word in the version:

Suggested change

	MARKDOWN = $(shell if [ `pandoc -v | head -n1 | cut -d" " -f2 | head -c1` -ge "2" ]; then echo markdown-smart; else echo markdown; fi)
	MARKDOWN = $(shell printf 'markdown%s\n' "$(pandoc -v | { read -r _ x; x=${x%%[^0-9]*}; [ "${x:-0}" -ge 2 ] && printf '%s' "-smart"; })")