bcache-tools: add name to the source store path

So that

 $ nix-build -A bcache-tools.src

gives

 /nix/store/HASH-bcache-tools-1.0.7.tar.gz

instead of

 /nix/store/HASH-v1.0.7.tar.gz

pkgs/tools/filesystems/bcache-tools/default.nix

@@ -5,6 +5,7 @@ stdenv.mkDerivation rec {
   version = "1.0.7";
 
   src = fetchurl {
+    name = "${name}.tar.gz";
     url = "https://github.com/g2p/bcache-tools/archive/v${version}.tar.gz";
     sha256 = "1gbsh2qw0a7kgck6w0apydiy37nnz5xvdgipa0yqrfmghl86vmv4";
   };