textproc/libxlsxwriter: update to 0.8.6

Upstream changes:
- Fixed issue where images that started in hidden rows/columns weren't
  placed correctly in the worksheet.
- Fixed the mime-type reported by system file(1). The mime-type
  reported by "file --mime-type"/magic was incorrect for XlsxWriter
  files since it expected the [Content_types] to be the first file in
  the zip container.

Package changes:
- Fixed libxlsxwriter.so not picking up libz.so from buildlink.

(sjmulder)