Fix deprecations for nixos 20.09

configuration.nix

@@ -19,11 +19,9 @@
 
   networking.networkmanager.enable = true;
 
-  i18n = {
-    consoleFont = "Lat2-Terminus16";
-    consoleKeyMap = "us";
-    defaultLocale = "en_US.UTF-8";
-  };
+  console.font = "Lat2-Terminus16";
+  console.keyMap = "us";
+  i18n.defaultLocale = "en_US.UTF-8";
 
   # Set your time zone.
   time.timeZone = "Asia/Tokyo";