message: docs(changelog): 2.2.8
diff: # Changelog
  +### [v2.2.8](https://github.com/youzan/vant/tree/v2.2.8)
  +`2019-10-17`
  +
  +**Features**
  +
  +- Dialog: update border radius [\#4730](https://github.com/youzan/vant/pull/4730)
  +- Uploader: update delete icon style [\#4712](https://github.com/youzan/vant/pull/4712)
  +- Field: add show-word-limit prop [\#4721](https://github.com/youzan/vant/pull/4721)
  +- Stepper: limit decimal length when input [\#4747](https://github.com/youzan/vant/pull/4747)
  +- Slider: improve click area [\#4701](https://github.com/youzan/vant/pull/4701)
  +- ActionSheet: add description prop [\#4691](https://github.com/youzan/vant/pull/4691)
  +- Slider: add slide animation [\#4700](https://github.com/youzan/vant/pull/4700)
  +- add gradient color variables [\#4752](https://github.com/youzan/vant/pull/4752)
  +- add multi-line ellipsis classes [\#4690](https://github.com/youzan/vant/pull/4690)
  +
  +**Bug Fixes**
  +
  +- fix AddressEdit area confirmation verification [\#4724](https://github.com/youzan/vant/pull/4724)
  +- fix Rate incorrect height caused by inline-block [\#4693](https://github.com/youzan/vant/pull/4693)
  +- fix Slider pseudo element may casue body overflow-x [\#4699](https://github.com/youzan/vant/pull/4699)
  +
  +
  ### [v2.2.7](https://github.com/youzan/vant/tree/v2.2.7)
  `2019-10-11`
  