fix all picker's transition and styles, including select, autocomplete, timer-picker, date-picker
and so on, which transition should be 'el-zoom-in-top' and without duplication.
* style(slider): slider button style change
slider button add box-sizing: border-box and change the default size to make sure the style is the
same of before.
* style(slider): remove outline
* fix(docs): replace error v-slot/slot to correct
Replace all `v-slot` to `#default`, `v-slot:xxx` to `#xxx`, `slot="xxx"` to `#xxx`.
fix#704
* docs: v-slot can not bind on div
* fix: fix v-slot
