Update cachix with new naming conventions

modules/cachix.nix

@@ -3,11 +3,13 @@
 
 {
   nix = {
-    binaryCaches = [
-      "https://nix-community.cachix.org"
-    ];
-    binaryCachePublicKeys = [
-      "nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs="
-    ];
+    settings = {
+      substituters = [
+        "https://nix-community.cachix.org"
+      ];
+      trusted-public-keys = [
+        "nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs="
+      ];
+    };
   };
 }