book: update sl

Updated via the `update-book.yml` GitHub workflow.

Author: ttaylorr

external/book/content/book/sl/v2/_index.html

@@ -8,7 +8,7 @@
   language_code: sl
   front_page: true
   repository_url: https://github.com/progit/progit2-sl
-  sha: 29736b65e994e23029842375b340ad48eb4f5b75
+  sha: 87ad425db2ca5879d3960b33c8dc7968782df82d
 page_title: Git - Book
 url: "/book/sl/v2.html"
 aliases:

external/book/sync/book-sl.sha

@@ -1 +1 @@
-29736b65e994e23029842375b340ad48eb4f5b75
+87ad425db2ca5879d3960b33c8dc7968782df82d