bootstrap4示例模板中出现这样的代码
<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
这行代码的作用可以让网页的宽度自动适应手机屏幕的宽度，但是多了shrink-to-fit=no，
这是什么鬼？查找文档得知，主要是为了兼容iOS9
Viewport meta tags using
"width=device-width"cause the page to scale down to fit content that overflows the viewport bounds. You can override this behavior by adding"shrink-to-fit=no"to your meta tag as shown below. The added value will prevent the page from scaling to fit the viewport.