gnu: alex4: Don't use unstable tarball.

* gnu/packages/games.scm (alex4)[source]: Use GIT-FETCH and
GIT-FILE-NAME.

gnu/packages/games.scm

@@ -256,11 +256,13 @@ mouse and joystick control, and original music.")
     (version "1.2-alpha")
     (source
      (origin
-       (method url-fetch)
-       (uri (string-append "https://github.com/carstene1ns/alex4/archive/"
-                           version ".tar.gz"))
+       (method git-fetch)
+       (uri (git-reference
+             (url "https://github.com/carstene1ns/alex4.git")
+             (commit version)))
+       (file-name (git-file-name name version))
        (sha256
-        (base32 "0jj1g3v1a6lyfwp5g2ly0n9z65ryqck8jxvzr01kaqjj3lsfkrhg"))))
+        (base32 "104nlhdsv1sg9g08fh5adwazw80400081awy7jsrn842srca0q1f"))))
     (build-system gnu-build-system)
     (arguments
      `(#:tests? #f                      ; no check target