workrave: fix version format and tarball name

pkgs/applications/misc/workrave/default.nix

···
   gdome2, gstreamer, libsigcxx }:
 
 stdenv.mkDerivation rec {
-  version = "v1_10_6";
+  version = "1.10.6";
   name = "workrave-${version}";
 
-  src = fetchurl {
-    url = "http://github.com/rcaelers/workrave/archive/${version}.tar.gz";
+  src = let
+    version_ = with stdenv.lib;
+      concatStringsSep "_" (splitString "." version);
+  in fetchurl {
+    name = "${name}.tar.gz";
+    url = "http://github.com/rcaelers/workrave/archive/v${version_}.tar.gz";
     sha256 = "0q2p83n33chbqzdcdm7ykfsy73frfi6drxzm4qidxwzpzsxrysgq";
   };