chore: Translate pressbooks-book.pot in es

27% of minimum 25% translated source file: 'pressbooks-book.pot'
on 'es'.

Sync of partially translated files: 
untranslated content is included with an empty translation 
or source language content depending on file format

languages/pressbooks-book-es_ES.po

@@ -186,11 +186,11 @@ msgstr "Mostrar las imágenes enlazadas en una caja de luz"
 
 #: inc/filters/namespace.php:19
 msgid "Private"
-msgstr ""
+msgstr "Privado"
 
 #: inc/helpers/namespace.php:145
 msgid "Public Domain"
-msgstr ""
+msgstr "Dominio público"
 
 #: inc/helpers/namespace.php:148
 msgid "Creative Commons Attribution"