Added disc as default list style

Author: GabrielAraujo

lib/src/style.dart

@@ -664,7 +664,7 @@ enum ListStyleType {
   factory ListStyleType.fromName(String name) {
     return ListStyleType.values.firstWhere((value) {
       return name == value.counterStyle;
-    });
+    }, orElse: () => ListStyleType.disc);
   }
 }