textproc/hs-pandoc-crossref: Update 0.3.18.2 => 0.3.21

Changelogs:

• https://hackage.haskell.org/package/pandoc-crossref-0.3.21/changelog

• Pet portclippy(1) and portfmt(1)

Approved by: haskell@ (alven@)
Approved by: yuri@ (Mentor)

Differential Revision: https://reviews.freebsd.org/D52811