overlay: override btrbk with latest master

nix/overlays/overrides.nix

@@ -44,4 +44,24 @@ in {
       keyring
     ]);
   });
+
+  btrbk = super.btrbk.overrideAttrs(attrs: rec {
+    version = "0.30.0";
+    src =  builtins.fetchurl {
+      url = "https://digint.ch/download/btrbk/releases/${attrs.pname}-${version}.tar.xz";
+      sha256 = "1wlp0z0ijv3cr155kp9c5l16dz4jf8h897ddnawaj9rj1zgfk9z8";
+    };
+
+    # version = "2020-12-30";
+    # src = builtins.fetchurl {
+    #   url = "https://github.com/digint/btrbk/archive/dd5991099ad778a3e0c5d11c770ad169c3095068.tar.gz";
+    #   sha256 = "0iyjgr1nv1n7mpsrgkrmb85sz3ycimmfvvhj08cvkjgl0r1762sb";
+    # };
+
+    preFixup = ''
+      wrapProgram $out/bin/btrbk \
+        --set PERL5LIB $PERL5LIB \
+        --prefix PATH ':' "${self.stdenv.lib.makeBinPath (with self; [ btrfs-progs bash mbuffer openssh ])}"
+    '';
+  });
 }