message: [changelog] 1.1.1
diff: ## Changelog
  +### [1.1.1](https://github.com/youzan/vant/tree/v1.1.1)
  +`2018-05-04`
  +
  +**Improvements**
  +
  +* Contact: optimize background image [\#972](https://github.com/youzan/vant/pull/972) [@chenjiahan](https://github.com/chenjiahan)
  +* List: add loading-text prop [\#948](https://github.com/youzan/vant/pull/948) [@rex-zsd](https://github.com/rex-zsd)
  +* Swipe: optimzie performance [\#985](https://github.com/youzan/vant/pull/985) [@chenjiahan](https://github.com/chenjiahan)
  +* Swipe: add touchable prop [\#975](https://github.com/youzan/vant/pull/975) [@chenjiahan](https://github.com/chenjiahan)
  +* Swipe: support vertical mode [\#938](https://github.com/youzan/vant/pull/938) [@jerryni](https://github.com/jerryni)
  +* Slider: expand touch area [\#977](https://github.com/youzan/vant/pull/977) [@chenjiahan](https://github.com/chenjiahan)
  +* Stepper: add interger prop [\#951](https://github.com/youzan/vant/pull/951) [@chenjiahan](https://github.com/chenjiahan)
  +* Tab: add line-width prop [\#988](https://github.com/youzan/vant/pull/988) [@chenjiahan](https://github.com/chenjiahan)
  +
  +**Bug Fixes**
  +* fix ImagePreview offset calc error [\#980](https://github.com/youzan/vant/pull/980) [@jerryni](https://github.com/jerryni)
  +* fix Search incomplete text display in iOS [\#974](https://github.com/youzan/vant/pull/974) [@chenjiahan](https://github.com/chenjiahan)
  +
  +
  ### [1.1.0](https://github.com/youzan/vant/tree/v1.1.0)
  `2018-04-25`
  