plans-coding

Select tag as multiple when size is equal to 1

1

### Prerequisites - [x] I have [searched](https://github.com/twbs/bootstrap/issues?utf8=%E2%9C%93&q=is%3Aissue) for duplicate or closed issues - [x] I have [validated](https://html5.validator.nu/) any HTML to avoid common problems - [x] I have read the [contributing...