message: Update api-specific.md
diff: -# Methods / Customized
  +# Specific API
  -better-scroll also supports several customized methods to implement some specific feature.
  +better-scroll also have several specific API to help you implement customized features.
  ## goToPage(x, y, time, easing)
  - Parameters:
  - - {Number} x, number of horizontal axis page.
  - - {Number} y, number of vertical axis page.
  - - {Number} time, animation duration.
  - - {Object} easing, easing function, usually don't suggest modifying. If you really need to modify, please consult the format of ease.js in source code.
  + - `{Number} x`, number of horizontal axis page.
  + - `{Number} y`, number of vertical axis page.
  + - `{Number} time`, animation duration.
  + - `{Object} easing`, easing function, usually don't suggest modifying. If you really need to modify, please consult the format of ease.js in source code.
  - Return: none.
  - Usage: in slide component, slide usually has several pages. Use this method scroll to specific page.
  ## next(time, easing)
  - Parameters:
  - - {Number} time animation duration.
  - - {Object} easing, easing function, usually don't suggest modifying. If you really need to modify, please consult the format of ease.js in source code.
  + - `{Number} time`, animation duration.
  + - `{Object} easing`, easing function, usually don't suggest modifying. If you really need to modify, please consult the format of ease.js in source code.
  - Return: none.
  - Usage: scroll to next page.
  ## prev(time, easing)
  - Parameters:
  - - {Number} time, animation duration.
  - - {Object} easing, easing function, usually don't suggest modifying. If you really need to modify, please consult the format in ease.js of source code.
  + - `{Number} time`, animation duration.
  + - `{Object} easing`, easing function, usually don't suggest modifying. If you really need to modify, please consult the format in ease.js of source code.
  - Return: none.
  - Usage: scroll to previous page.
  ## getCurrentPage()
  - Parameters: none.
  - - Return: {Object} `{ x: posX, y: posY,pageX: x, pageY: y}`
  - - x: coordinate of current page on horizontal axis.
  - - y: coordinate of current page on vertical axis.
  - - pageX: page number on horizontal axis.
  - - pageY: page number on vertical axis.
  + - Return: `{Object}`, like `{ x: posX, y: posY,pageX: x, pageY: y}`
  + - `x`: coordinate of current page on horizontal axis.
  + - `y`: coordinate of current page on vertical axis.
  + - `pageX`: page number on horizontal axis.
  + - `pageY`: page number on vertical axis.
  - Usage: get information of current page.
  ## wheelTo(index)
  - Parameters:
  - - {Number} index.
  + - `{Number} index`.
  - Return: none.
  - Usage: in picker component, use this methods scrolling to the indexed position.
  ## getSelectedIndex()
  - Parameters: none.
  - - Return: {Number} current selected index.
  + - Return: `{Number}` current selected index.
  - Usage: get current selected index.
  ## finishPullDown()
  