message: use different regex for determining a watchable model
diff: @@ -168,7 +168,8 @@ export default class Generator {
  return null;
  }
  - const watchable = /^[a-z_]+[0-9]*(\w*\.[a-z_]\w*)*$/i.test(model.expression) && hasPath(model.expression, vnode.context);
  + // https://github.com/vuejs/vue/blob/dev/src/core/util/lang.js#L26
  + const watchable = !/[^\w.$]/.test(model.expression) && hasPath(model.expression, vnode.context);
  const lazy = !!(model.modifiers && model.modifiers.lazy);
  if (!watchable) {
  return { expression: null, lazy };
  