Minor error in htmlBlockType7Regexp

[maxb]

In https://github.com/yuin/goldmark/blob/master/parser/html_block.go:

var htmlBlockType7Regexp = regexp.MustCompile(`^[ ]{0,3}<(/)?([a-zA-Z0-9\-]+)(` + attributePattern + `*)(:?>|/>)\s*\n?$`)

Near the end, (:?>|/>) looks like a typo for (?:>|/>) (which could be more simply expressed as /?>)

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[maxb]

Not stale, still needs fixing