gnu: Add ruby-marcel.

Required for ruby-activestorage.

* gnu/packages/ruby.scm (ruby-marcel): New variable.

gnu/packages/ruby.scm

@@ -2960,6 +2960,30 @@ Ruby.  It simplifies the generation of complex SQL queries and adapts to
 various relational database implementations.")
     (license license:expat)))
 
+(define-public ruby-marcel
+  (package
+    (name "ruby-marcel")
+    (version "0.3.3")
+    (source
+     (origin
+       (method url-fetch)
+       (uri (rubygems-uri "marcel" version))
+       (sha256
+        (base32
+         "1nxbjmcyg8vlw6zwagf17l9y2mwkagmmkg95xybpn4bmf3rfnksx"))))
+    (build-system ruby-build-system)
+    (arguments
+     '(;; No included tests
+       #:tests? #f))
+    (propagated-inputs
+     `(("ruby-mimemagic" ,ruby-mimemagic)))
+    (synopsis "MIME type detection using magic numbers, filenames and extensions")
+    (description
+     "@code{marcel} provides @acronym{MIME, Multipurpose Internet Mail
+Extensions} type detection using magic numbers, filenames, and extensions")
+    (home-page "https://github.com/basecamp/marcel")
+    (license license:expat)))
+
 (define-public ruby-minitar
   ;; We package from the GitHub source to fix the security issue reported at
   ;; https://github.com/halostatue/minitar/issues/16.