versions: bump to 20.09 and improve NIX_PATH assembly

The NIX_PATH assembly now walks over all keys in the given channel
repositories and assembles a NIX_PATH entry from it. Previously it made
assumptions about a set of hardcoded keys being available, which wasn't
ideal as it didn't allow device-entries.

nix/os/devices/steveej-rmvbl-sdep0/configuration.nix

@@ -1,6 +1,10 @@
 { ... }:
 
 {
+  nixpkgs.config.packageOverrides = pkgs: with pkgs; {
+    nixPath = (import ../../../default.nix { versionsPath = ./versions.nix; }).nixPath;
+  };
+
   imports = [
     ../../profiles/common/configuration.nix
     ../../profiles/graphical/configuration.nix

nix/os/devices/steveej-rmvbl-sdep0/versions.nix

@@ -1,20 +1,30 @@
+let
+  nixpkgs = {
+    url = "https://github.com/NixOS/nixpkgs/";
+    ref = "nixos-20.09";
+    rev = "51aaa3fa1b69559456f9bd4968bd5b179a784f67";
+  };
+in
+
 {
-  channelsNixosStable = {
-    ref = "nixos-20.03";
-    rev = "5659cb448e9b615d642c5fe52779c2223e72f7eb";
+  inherit nixpkgs;
+  nixos = nixpkgs // {
+    suffix = "/nixos";
   };
-  channelsNixosUnstable = {
+  "channels-nixos-stable" = nixpkgs;
+  "channels-nixos-unstable" = {
+    url = "https://github.com/NixOS/nixpkgs/";
     ref = "nixos-unstable";
-    rev = "daaa0e33505082716beb52efefe3064f0332b521";
+    rev = "24c9b05ac53e422f1af81a156f1fd58499eb27fb";
   };
-  nixpkgsMaster = {
+  "nixpkgs-master" = {
     url = "https://github.com/NixOS/nixpkgs/";
     ref = "master";
-    rev = "55dc3b76f0ca1dd62d158b92a637fe484df5227d";
+    rev = "396f3407a28a0ce8ee537d6f4440d3e6cb359570";
   };
-  homeManagerModule = {
-    url = "https://github.com/rycee/home-manager";
-    ref = "release-20.03";
-    rev = "e6f96b6aa3e99495f9f6f3488ecf78dd316e5bec";
+  "home-manager-module" = {
+    url = "https://github.com/nix-community/home-manager";
+    ref = "release-20.09";
+    rev = "7339784e07217ed0232e08d1ea33b610c94657d8";
   };
 }