fix: add missing versions

pkgs/tools/audio/gvolicon/default.nix

@@ -1,7 +1,7 @@
 { stdenv, makeWrapper, alsaLib, pkgconfig, fetchgit, gnome3, gdk_pixbuf, librsvg }:
 
 stdenv.mkDerivation {
-  name = "gvolicon";
+  name = "gvolicon-2014-04-28";
   src = fetchgit {
     url = "https://github.com/Unia/gvolicon";
     rev = "c04cafb88124e1e5edc61dd52f76bf13381d5167";

pkgs/tools/audio/pa-applet/default.nix

@@ -1,7 +1,7 @@
 { stdenv, fetchgit, libpulseaudio, pkgconfig, gtk3, glibc, autoconf, automake, libnotify, libX11, xf86inputevdev }:
 
 stdenv.mkDerivation rec {
-  name = "pa-applet";
+  name = "pa-applet-2012-04-11";
 
   src = fetchgit {
     url = "git://github.com/fernandotcl/pa-applet.git";

pkgs/tools/audio/pnmixer/default.nix

@@ -1,7 +1,7 @@
 { stdenv, fetchgit, alsaLib, pkgconfig, gtk3, glibc, autoconf, automake, libnotify, libX11, gettext }:
 
 stdenv.mkDerivation rec {
-  name = "pnmixer";
+  name = "pnmixer-2014-07-24";
 
   src = fetchgit {
     url = "git://github.com/nicklan/pnmixer.git";