nixos/modules: Remove all usages of types.string

And replace them with a more appropriate type

Also fix up some minor module problems along the way

nixos/modules/services/misc/cpuminer-cryptonight.nix

@@ -28,15 +28,15 @@ in
         '';
       };
       url = mkOption {
-        type = types.string;
+        type = types.str;
         description = "URL of mining server";
       };
       user = mkOption {
-        type = types.string;
+        type = types.str;
         description = "Username for mining server";
       };
       pass = mkOption {
-        type = types.string;
+        type = types.str;
         default = "x";
         description = "Password for mining server";
       };
@@ -63,4 +63,4 @@ in
 
   };
 
-}
+}