gnu: ocaml-ppx-tools: Don't use unstable tarball.

* gnu/packages/ocaml.scm (ocaml-ppx-tools)[source]: Use GIT-FETCH and
GIT-FILE-NAME.
Fix indentation.

gnu/packages/ocaml.scm

@@ -1949,11 +1949,12 @@ simple (yet expressive) query language to select the tests to run.")
     (version "5.1+4.06.0")
     (source
      (origin
-        (method url-fetch)
-        (uri (string-append "https://github.com/alainfrisch/ppx_tools/archive/"
-                            version ".tar.gz"))
+       (method git-fetch)
+       (uri (git-reference
+             (url "https://github.com/alainfrisch/ppx_tools.git")
+             (commit version)))
        (sha256 (base32
-                  "0mncpy9v2mcjgnj7s2vqpp2b1ixv54djicfx66ic9wny9d202gj1"))))
+                "1ww4cspdpgjjsgiv71s0im5yjkr3544x96wsq1vpdacq7dr7zwiw"))))
     (build-system ocaml-build-system)
     (arguments
      `(#:phases (modify-phases %standard-phases (delete 'configure))