Update cachix with new naming conventions

modules/cachix.nix

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