message: [changelog] 1.6.13
diff: ## Changelog
  +## [v1.6.13](https://github.com/youzan/vant/tree/v1.6.13)
  +`2019-04-06`
  +
  +**Improvements**
  +
  +- Uploader: add name prop [\#3096](https://github.com/youzan/vant/pull/3096)
  +- Slider: add vertical prop [\#3078](https://github.com/youzan/vant/pull/3078)
  +- Stepper: add input-width prop [\#3076](https://github.com/youzan/vant/pull/3076)
  +- Tag: add less vars [\#3087](https://github.com/youzan/vant/pull/3087)
  +- Button: add less vars [\#3093](https://github.com/youzan/vant/pull/3093)
  +- CellGroup: add less vars [\#3094](https://github.com/youzan/vant/pull/3094)
  +
  +**Bug Fixes**
  +
  +- fix Tab should set line position when activated [\#3097](https://github.com/youzan/vant/pull/3097)
  +
  +
  ## [v1.6.12](https://github.com/youzan/vant/tree/v1.6.12)
  `2019-03-28`
  