nixos/amuled: add types

nixos/modules/services/networking/amuled.nix

@@ -24,6 +24,7 @@ in
       };
 
       dataDir = mkOption {
+        type = types.str;
         default = ''/home/${user}/'';
         description = ''
           The directory holding configuration, incoming and temporary files.
@@ -31,6 +32,7 @@ in
       };
 
       user = mkOption {
+        type = types.nullOr types.str;
         default = null;
         description = ''
           The user the AMule daemon should run as.