Update free-programming-books-langs.md (#9296)

Versioned APIs with Phoenix isn't available on the author's website anymore.

books/free-programming-books-langs.md

@@ -713,7 +713,7 @@ Books on general-purpose programming that don't focus on a specific language are
 #### Phoenix
 
 * [Phoenix Framework Guide](https://hexdocs.pm/phoenix/overview.html) (HTML)
-* [Versioned APIs with Phoenix](https://elviovicosa.com/freebies/versioned-apis-with-phoenix-by-elvio-vicosa.pdf) - Elvio Vicosa (PDF)
+* [Versioned APIs with Phoenix](https://web.archive.org/web/20210309052043/https://elviovicosa.com/freebies/versioned-apis-with-phoenix-by-elvio-vicosa.pdf) - Elvio Vicosa (PDF) *(:card_file_box: archived)*
 
 
 ### Embedded Systems