graphics/plutovg: Update 1.3.0 => 1.3.1

Changelogs:

• https://github.com/sammycage/plutovg/releases/tag/v1.3.1
• https://github.com/sammycage/plutovg/compare/v1.3.0...v1.3.1

Approved by: yuri@ (Mentor)

Differential Revision: https://reviews.freebsd.org/D52518