message: fix(core scroll): plugin don't work if BScroll.use is repeatedly called
diff: @@ -37,11 +37,13 @@ export default class BScroll extends EventEmitter {
  warn(
  `Plugin Class must specify plugin's name in static property by 'pluginName' field.`
  )
  + return
  }
  if (BScroll.usePluginSet[name]) {
  warn(
  `This plugin has been registered, maybe you need change plugin's name`
  )
  + return
  }
  BScroll.usePluginSet[name] = true
  BScroll.usePluginArray.push({
  