message: fix(core): remove set
diff: @@ -11,7 +11,9 @@ interface PluginItem {
  enforce?: EnforceOrder.Pre | EnforceOrder.Post
  ctor: PluginCtor
  }
  -
  +interface PluginSet {
  + [key: string]: boolean
  +}
  interface PropertyConfig {
  key: string
  sourceKey: string
  @@ -20,7 +22,7 @@ interface PropertyConfig {
  export default class BScroll extends EventEmitter {
  static readonly version: string = '2.0.0'
  static usePluginArray: PluginItem[] = []
  - static usePluginSet: Set<string> = new Set()
  + static usePluginSet: PluginSet = {}
  scroller: Scroller
  options: Options
  hooks: EventEmitter
  @@ -36,12 +38,12 @@ export default class BScroll extends EventEmitter {
  `Plugin Class must specify plugin's name in static property by 'name' field.`
  )
  }
  - if (BScroll.usePluginSet.has(name)) {
  + if (BScroll.usePluginSet[name]) {
  warn(
  `This plugin has been registered, maybe you need change plugin's name`
  )
  }
  - BScroll.usePluginSet.add(name)
  + BScroll.usePluginSet[name] = true
  BScroll.usePluginArray.push({
  name,
  enforce: ctor.enforce,
  