The latest bootstrap version is 3.1.1.
But currently the yii2-bootstrap is depends on bootstrap 3.0.*.
Both yii2-gii and yii2-debug are depend on yii2-bootstrap.
Change the code within vendor folder directly is absolutely a bad idea.
So what is the recommended way to upgrade to the latest bootstrap version?
The bootstrap library is also under active development, it is always changing. I think it would be nice if the Yii2 framework can provide a easy way to let developers upgrade the bootstrap version themselves.