book: update nl

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

Author: dscho

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

@@ -8,7 +8,7 @@
   language_code: nl
   front_page: true
   repository_url: https://github.com/progit/progit2-nl
-  sha: d80f1205037e5387107ca5afc74d757c504b3b56
+  sha: 51a7c8c528fa0f1c2f9173d1d699b50c978ec9ef
   ebook_pdf: https://github.com/progit/progit2-nl/releases/download/2.1.117/progit.pdf
   ebook_epub: https://github.com/progit/progit2-nl/releases/download/2.1.117/progit.epub
 page_title: Git - Book

external/book/sync/book-nl.sha

@@ -1 +1 @@
-d80f1205037e5387107ca5afc74d757c504b3b56
+51a7c8c528fa0f1c2f9173d1d699b50c978ec9ef