gnu: Add rust-downcast-0.10.

* gnu/packages/crates-io.scm (rust-downcast-0.10): New variable.

Signed-off-by: Nicolas Goaziou <mail@nicolasgoaziou.fr>

gnu/packages/crates-io.scm

@@ -14453,6 +14453,27 @@ from macros.")
         ("rust-rustc-serialize" ,rust-rustc-serialize-0.3)
         ("rust-strsim" ,rust-strsim-0.5))))))
 
+(define-public rust-downcast-0.10
+  (package
+    (name "rust-downcast")
+    (version "0.10.0")
+    (source
+     (origin
+       (method url-fetch)
+       (uri (crate-uri "downcast" version))
+       (file-name (string-append name "-" version ".tar.gz"))
+       (sha256
+        (base32 "07bh0l95gwrzak6rj29v8kkm577d8vivxsxhqgscf64b4bq59d2b"))))
+    (build-system cargo-build-system)
+    (arguments `(#:skip-build? #t))
+    (home-page "https://github.com/fkoep/downcast-rs")
+    (synopsis
+     "Trait for downcasting trait objects back to their original types")
+    (description
+     "This crate provides a trait for downcasting trait objects back to their
+original types.")
+    (license license:expat)))
+
 (define-public rust-downcast-rs-1
   (package
     (name "rust-downcast-rs")