treewide: fix types for mkDerivation params

pkgs/tools/backup/lvmsync/default.nix

@@ -1,27 +1,22 @@
 { stdenv, bundlerEnv, ruby, bundlerUpdateScript, makeWrapper }:
 
-let
-
+stdenv.mkDerivation rec {
   pname = "lvmsync";
   version = (import ./gemset.nix).${pname}.version;
 
-in stdenv.mkDerivation rec {
-
-  name = "${pname}-${version}";
-
-  env = bundlerEnv {
-    name = "${pname}-${version}-gems";
-    ruby = ruby;
-    gemfile  = ./Gemfile;
-    lockfile = ./Gemfile.lock;
-    gemset   = ./gemset.nix;
-  };
-
   buildInputs = [ makeWrapper ];
 
   phases = ["installPhase"];
 
-  installPhase = ''
+  installPhase = let
+    env = bundlerEnv {
+      name = "${pname}-${version}-gems";
+      ruby = ruby;
+      gemfile  = ./Gemfile;
+      lockfile = ./Gemfile.lock;
+      gemset   = ./gemset.nix;
+    };
+  in ''
     mkdir -p $out/bin
     makeWrapper ${env}/bin/lvmsync $out/bin/lvmsync
   '';