gnu: emacs-avy: Don't use unstable tarball.

* gnu/packages/emacs-xyz.scm (emacs-avy)[source]: Use GIT-FETCH and
GIT-FILE-NAME.

gnu/packages/emacs-xyz.scm

@@ -4198,13 +4198,13 @@ show icons as well.")
     (version "0.4.0")
     (source
      (origin
-       (method url-fetch)
-       (uri (string-append "https://github.com/abo-abo/avy/archive/"
-                           version ".tar.gz"))
-       (file-name (string-append name "-" version ".tar.gz"))
+       (method git-fetch)
+       (uri (git-reference
+             (url "https://github.com/abo-abo/avy.git")
+             (commit version)))
+       (file-name (git-file-name name version))
        (sha256
-        (base32
-         "1wdrq512h25ymzjbf2kbsdymvd2ryfwzb6bh5bc3yv7q203im796"))))
+        (base32 "0rq9ab264565z83cly743nbhrd9m967apmnlhqr1gy8dm4hcy7nm"))))
     (build-system emacs-build-system)
     (home-page "https://github.com/abo-abo/avy")
     (synopsis "Tree-based completion for Emacs")