textproc/sigil: update to 1.4.2

From ChangeLog: https://sigil-ebook.com/2020/11/21/sigil-1-4-2-critical-fix-release/

Bug Fixes Since Sigil-1.4.0:

• critical bug fix for incorrectly xml encoding of opf metadata attributes that use entities
• fix bug in "Add Existing" files when file names would require percent encoding
• fix bug in multiple language spellchecking dialog word lookup when no language attributes used
• update de, nl, sv, ko, ru translations that missed the Sigil 1.4.0 initial release
• critical bug fix for over xml encoding html used inside metadata in the opf
• revert ctrl-f to it long standing Find and Replace behaviour

If you are using either Sigil-1.4.0 or Sigil-1.4.1, we strongly urge you to
upgrade to Sigil-1.4.2.

PR: 251322
Submitted by: jonc@chen.org.nz (maintainer)