版本：
文件：
- https://cdn.bootcdn.net/ajax/libs/placeholder-shiv/0.2/placeholder-shiv.jquery.js
- https://cdn.bootcdn.net/ajax/libs/placeholder-shiv/0.2/placeholder-shiv.jquery.min.js
- https://cdn.bootcdn.net/ajax/libs/placeholder-shiv/0.2/placeholder-shiv.js
- https://cdn.bootcdn.net/ajax/libs/placeholder-shiv/0.2/placeholder-shiv.min.js