message: docs(changelog): 2.1.5
diff: # Changelog
  +### [v2.1.5](https://github.com/youzan/vant/tree/v2.1.5)
  +`2019-08-23`
  +
  +**Improvements**
  +
  +- Toast: add closeOnClick option [\#4192](https://github.com/youzan/vant/pull/4192)
  +- Uploader: add image-fit prop [\#4189](https://github.com/youzan/vant/pull/4189)
  +- Uploader: add click-preview event [\#4206](https://github.com/youzan/vant/pull/4206)
  +- Uploader: add preview-full-image prop [\#4205](https://github.com/youzan/vant/pull/4205)
  +- DropdownMenu: add @dropdown-menu-title-active-text-color less var [\#4208](https://github.com/youzan/vant/pull/4208)
  +
  +**Bug Fixes**
  +
  +- fix IndexBar sticky bug [\#4184](https://github.com/youzan/vant/pull/4184)
  +- fix NumberKeyboard border color [\#4183](https://github.com/youzan/vant/pull/4183)
  +- fix Area can't select some oversea countries [\#4195](https://github.com/youzan/vant/pull/4195)
  +
  +
  +
  ### [v2.1.4](https://github.com/youzan/vant/tree/v2.1.4)
  `2019-08-21`
  