Add mu 1.6.4 patch

patches/135080.patch

@@ -0,0 +1,29 @@
+From c9fc9cb5e386add817e49cba119bff6fb5b77e0d Mon Sep 17 00:00:00 2001
+From: Charlotte Van Petegem <charlotte@vanpetegem.me>
+Date: Sat, 21 Aug 2021 16:53:46 +0200
+Subject: [PATCH] mu: 1.6.3 -> 1.6.4
+
+---
+ pkgs/tools/networking/mu/default.nix | 4 ++--
+ 1 file changed, 2 insertions(+), 2 deletions(-)
+
+diff --git a/pkgs/tools/networking/mu/default.nix b/pkgs/tools/networking/mu/default.nix
+index 468bc127228a76..694c1f5e721f48 100644
+--- a/pkgs/tools/networking/mu/default.nix
++++ b/pkgs/tools/networking/mu/default.nix
+@@ -7,13 +7,13 @@
+ 
+ stdenv.mkDerivation rec {
+   pname = "mu";
+-  version = "1.6.3";
++  version = "1.6.4";
+ 
+   src = fetchFromGitHub {
+     owner  = "djcb";
+     repo   = "mu";
+     rev    = version;
+-    sha256 = "hmP2bcoBWMd2GZBE8XtJ5QePpWnkJV5pu69aDmL5V4g=";
++    sha256 = "rRBi6bgxkVQ94wLBqVQikIE0jVkvm1fjtEzFMsQTJz8=";
+   };
+ 
+   postPatch = lib.optionalString (batchSize != null) ''