anbox: 2020-11-29 -> 2021-10-20, fix build

pkgs/os-specific/linux/anbox/default.nix

···
 
 stdenv.mkDerivation rec {
   pname = "anbox";
-  version = "unstable-2020-11-29";
+  version = "unstable-2021-10-20";
 
   src = fetchFromGitHub {
     owner = pname;
     repo = pname;
-    rev = "6c10125a7f13908d2cbe56d2d9ab09872755f265";
-    sha256 = "00bqssh4zcs0jj6w07b91719xkrpdw75vpcplwrvlhwsvl55f901";
+    rev = "84f0268012cbe322ad858d76613f4182074510ac";
+    sha256 = "sha256-QXWhatewiUDQ93cH1UZsYgbjUxpgB1ajtGFYZnKmabc=";
     fetchSubmodules = true;
   };